Add section on how to run tests

README.md

@@ -56,6 +56,18 @@ Maintainers ([@open-telemetry/python-maintainers](https://github.com/orgs/open-t
 
 *Find more about the maintainer role in [community repository](https://github.com/open-telemetry/community/blob/master/community-membership.md#maintainer).*
 
+## Running Tests Locally
+
+1. Go to your Contrib repo directory. `cd ~/git/opentelemetry-python-contrib`.
+2. Create a virtual env in your Contrib repo directory. `python3 -m venv my_test_venv`.
+3. Activate your virtual env. `source my_test_venv/bin/activate`.
+4. Clone the [OpenTelemetry Python](https://github.com/open-telemetry/opentelemetry-python) Python Core repo to a folder named `opentelemetry-python-core`. `git clone git@github.com:open-telemetry/opentelemetry-python.git opentelemetry-python-core`.
+5. Change directory to the repo that was just cloned. `cd opentelemetry-python-core`.
+6. Move the head of this repo to the hash you want your tests to use. This is currently the tag `v0.15b0` as seen in `.github/workflows/test.yml`. Use `git fetch --tags && git checkout v0.15b0`.
+7. Go back to the root directory. `cd ../`.
+8. Make sure you have `tox` installed. `pip install tox`.
+9. Run tests for a package. (e.g. `tox -e test-instrumentation-flask`.)
+
 ### Thanks to all the people who already contributed!
 
 <a href="https://github.com/open-telemetry/opentelemetry-python-contrib/graphs/contributors">