Add clarifying comment to blacken nox target.

[yoshi-automation]

This PR was generated using Autosynth. 🌈

Here's the log from Synthtool:

synthtool > Executing /tmpfs/src/git/autosynth/working_repo/spanner/synth.py.
synthtool > Ensuring dependencies.
synthtool > Pulling artman image.
latest: Pulling from googleapis/artman
Digest: sha256:5fd9aee1d82a00cebf425c8fa431f5457539562f5867ad9c54370f0ec9a7ccaa
Status: Image is up to date for googleapis/artman:latest
synthtool > Cloning googleapis.
synthtool > Running generator for google/spanner/artman_spanner.yaml.
synthtool > Generated code into /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/python/spanner-v1.
synthtool > Copy: /home/kbuilder/.cache/synthtool/googleapis/google/spanner/v1/mutation.proto to /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/python/spanner-v1/google/cloud/spanner_v1/proto/mutation.proto
synthtool > Copy: /home/kbuilder/.cache/synthtool/googleapis/google/spanner/v1/spanner.proto to /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/python/spanner-v1/google/cloud/spanner_v1/proto/spanner.proto
synthtool > Copy: /home/kbuilder/.cache/synthtool/googleapis/google/spanner/v1/type.proto to /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/python/spanner-v1/google/cloud/spanner_v1/proto/type.proto
synthtool > Copy: /home/kbuilder/.cache/synthtool/googleapis/google/spanner/v1/keys.proto to /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/python/spanner-v1/google/cloud/spanner_v1/proto/keys.proto
synthtool > Copy: /home/kbuilder/.cache/synthtool/googleapis/google/spanner/v1/result_set.proto to /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/python/spanner-v1/google/cloud/spanner_v1/proto/result_set.proto
synthtool > Copy: /home/kbuilder/.cache/synthtool/googleapis/google/spanner/v1/transaction.proto to /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/python/spanner-v1/google/cloud/spanner_v1/proto/transaction.proto
synthtool > Copy: /home/kbuilder/.cache/synthtool/googleapis/google/spanner/v1/query_plan.proto to /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/python/spanner-v1/google/cloud/spanner_v1/proto/query_plan.proto
synthtool > Placed proto files into /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/python/spanner-v1/google/cloud/spanner_v1/proto.
synthtool > Replaced '# limitations under the License.\n\nimport google.api_core.grpc_helpers\n' in google/cloud/spanner_v1/gapic/transports/spanner_grpc_transport.py.
synthtool > Replaced 'from google.cloud.spanner_v1.proto import spanner_pb2_grpc\n' in google/cloud/spanner_v1/gapic/transports/spanner_grpc_transport.py.
synthtool > Replaced '(\\s+)return google.api_core.grpc_helpers.create_channel\\(\n' in google/cloud/spanner_v1/gapic/transports/spanner_grpc_transport.py.
synthtool > Replaced 'from google.cloud import spanner_v1' in tests/unit/gapic/v1/test_spanner_client_v1.py.
synthtool > Running generator for google/spanner/admin/instance/artman_spanner_admin_instance.yaml.
synthtool > Generated code into /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/python/spanner-admin-instance-v1.
synthtool > Copy: /home/kbuilder/.cache/synthtool/googleapis/google/spanner/admin/instance/v1/spanner_instance_admin.proto to /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/python/spanner-admin-instance-v1/google/cloud/spanner_admin_instance_v1/proto/spanner_instance_admin.proto
synthtool > Placed proto files into /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/python/spanner-admin-instance-v1/google/cloud/spanner_admin_instance_v1/proto.
synthtool > Replaced "'google-cloud-spanner-admin-instance'" in google/cloud/spanner_admin_instance_v1/gapic/instance_admin_client.py.
synthtool > Replaced 'from google\\.cloud\\.spanner\\.admin\\.instance_v1.proto' in google/cloud/spanner_admin_instance_v1/proto/spanner_instance_admin_pb2_grpc.py.
synthtool > Replaced '====*' in google/cloud/spanner_v1/proto/transaction_pb2.py.
synthtool > Replaced '----*' in google/cloud/spanner_v1/proto/transaction_pb2.py.
synthtool > Replaced '~~~~*' in google/cloud/spanner_v1/proto/transaction_pb2.py.
synthtool > Running generator for google/spanner/admin/database/artman_spanner_admin_database.yaml.
synthtool > Generated code into /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/python/spanner-admin-database-v1.
synthtool > Copy: /home/kbuilder/.cache/synthtool/googleapis/google/spanner/admin/database/v1/spanner_database_admin.proto to /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/python/spanner-admin-database-v1/google/cloud/spanner_admin_database_v1/proto/spanner_database_admin.proto
synthtool > Placed proto files into /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/python/spanner-admin-database-v1/google/cloud/spanner_admin_database_v1/proto.
synthtool > Replaced "'google-cloud-spanner-admin-database'" in google/cloud/spanner_admin_database_v1/gapic/database_admin_client.py.
synthtool > Replaced 'from google\\.cloud\\.spanner\\.admin\\.database_v1.proto' in google/cloud/spanner_admin_database_v1/proto/spanner_database_admin_pb2_grpc.py.
.coveragerc
.flake8
MANIFEST.in
noxfile.py.j2
setup.cfg
synthtool > Replaced 'include README.rst LICENSE\n' in MANIFEST.in.
Running session blacken
Creating virtualenv using python3.6 in /tmpfs/src/git/autosynth/working_repo/spanner/.nox/blacken
pip install --upgrade black
black google tests docs
reformatted /tmpfs/src/git/autosynth/working_repo/spanner/google/cloud/spanner_admin_database_v1/gapic/enums.py
reformatted /tmpfs/src/git/autosynth/working_repo/spanner/google/cloud/spanner_admin_database_v1/gapic/transports/database_admin_grpc_transport.py
reformatted /tmpfs/src/git/autosynth/working_repo/spanner/google/cloud/spanner_admin_database_v1/gapic/database_admin_client_config.py
reformatted /tmpfs/src/git/autosynth/working_repo/spanner/google/cloud/spanner_admin_instance_v1/gapic/enums.py
reformatted /tmpfs/src/git/autosynth/working_repo/spanner/google/cloud/spanner_admin_database_v1/proto/spanner_database_admin_pb2_grpc.py
reformatted /tmpfs/src/git/autosynth/working_repo/spanner/google/cloud/spanner_admin_instance_v1/gapic/instance_admin_client_config.py
reformatted /tmpfs/src/git/autosynth/working_repo/spanner/google/cloud/spanner_admin_instance_v1/gapic/transports/instance_admin_grpc_transport.py
reformatted /tmpfs/src/git/autosynth/working_repo/spanner/google/cloud/spanner_admin_database_v1/gapic/database_admin_client.py
reformatted /tmpfs/src/git/autosynth/working_repo/spanner/google/cloud/spanner_admin_instance_v1/gapic/instance_admin_client.py
reformatted /tmpfs/src/git/autosynth/working_repo/spanner/google/cloud/spanner_admin_database_v1/proto/spanner_database_admin_pb2.py
reformatted /tmpfs/src/git/autosynth/working_repo/spanner/google/cloud/spanner_admin_instance_v1/proto/spanner_instance_admin_pb2_grpc.py
reformatted /tmpfs/src/git/autosynth/working_repo/spanner/google/cloud/spanner_v1/gapic/enums.py
reformatted /tmpfs/src/git/autosynth/working_repo/spanner/google/cloud/spanner_v1/gapic/transports/spanner_grpc_transport.py
reformatted /tmpfs/src/git/autosynth/working_repo/spanner/google/cloud/spanner_v1/gapic/spanner_client_config.py
reformatted /tmpfs/src/git/autosynth/working_repo/spanner/google/cloud/spanner_v1/proto/keys_pb2_grpc.py
reformatted /tmpfs/src/git/autosynth/working_repo/spanner/google/cloud/spanner_v1/proto/keys_pb2.py
reformatted /tmpfs/src/git/autosynth/working_repo/spanner/google/cloud/spanner_v1/proto/mutation_pb2_grpc.py
reformatted /tmpfs/src/git/autosynth/working_repo/spanner/google/cloud/spanner_v1/gapic/spanner_client.py
reformatted /tmpfs/src/git/autosynth/working_repo/spanner/google/cloud/spanner_v1/proto/query_plan_pb2_grpc.py
reformatted /tmpfs/src/git/autosynth/working_repo/spanner/google/cloud/spanner_v1/proto/mutation_pb2.py
reformatted /tmpfs/src/git/autosynth/working_repo/spanner/google/cloud/spanner_admin_instance_v1/proto/spanner_instance_admin_pb2.py
reformatted /tmpfs/src/git/autosynth/working_repo/spanner/google/cloud/spanner_v1/proto/result_set_pb2_grpc.py
reformatted /tmpfs/src/git/autosynth/working_repo/spanner/google/cloud/spanner_v1/proto/spanner_pb2_grpc.py
reformatted /tmpfs/src/git/autosynth/working_repo/spanner/google/cloud/spanner_v1/proto/query_plan_pb2.py
reformatted /tmpfs/src/git/autosynth/working_repo/spanner/google/cloud/spanner_v1/proto/transaction_pb2_grpc.py
reformatted /tmpfs/src/git/autosynth/working_repo/spanner/google/cloud/spanner_v1/proto/result_set_pb2.py
reformatted /tmpfs/src/git/autosynth/working_repo/spanner/google/cloud/spanner_v1/proto/type_pb2_grpc.py
reformatted /tmpfs/src/git/autosynth/working_repo/spanner/google/cloud/spanner_v1/proto/type_pb2.py
reformatted /tmpfs/src/git/autosynth/working_repo/spanner/google/cloud/spanner_v1/proto/transaction_pb2.py
reformatted /tmpfs/src/git/autosynth/working_repo/spanner/tests/unit/gapic/v1/test_database_admin_client_v1.py
reformatted /tmpfs/src/git/autosynth/working_repo/spanner/tests/unit/gapic/v1/test_instance_admin_client_v1.py
reformatted /tmpfs/src/git/autosynth/working_repo/spanner/tests/unit/gapic/v1/test_spanner_client_v1.py
reformatted /tmpfs/src/git/autosynth/working_repo/spanner/google/cloud/spanner_v1/proto/spanner_pb2.py
All done! ✨ 🍰 ✨
33 files reformatted, 53 files left unchanged.
Session blacken was successful.
synthtool > Cleaned up 2 temporary directories.
synthtool > Wrote metadata to synth.metadata.