Add that no merges should happen between version updates

RELEASING.md

@@ -12,6 +12,8 @@ PRs that don't release new modules should look something like [#225](https://git
 
 3. Before moving on, verify that the artifacts have successfully been pushed to the Maven Central Repository.  Open Travis CI, click the ["Build History" tab](https://travis-ci.org/GoogleCloudPlatform/gcloud-java/builds), and open the second build's logs for Step 2's PR.  Be sure that you are not opening the "Pull Request" build logs.  When the build finishes, scroll to the end of the log and verify that the artifacts were successfully staged and deployed.  Search for `gcloud-java` on the [Sonatype website](https://oss.sonatype.org/#nexus-search;quick~gcloud-java) and check the latest version number.  In rare cases (when the Maven plugin that determines the version of the repository fails), the artifacts may not be deployed even if the version in the pom.xml files don't contain `SNAPSHOT`.  If the artifacts weren't deployed due to invalid version parsing or a flaky test, rerun the build.
 
+  Important: Do not merge in any pull requests between Steps 3 and 4. This will cause the artifacts to be redeployed and the website to be regenerated.
+
 4. Publish a release on Github manually.
 Go to the [releases page](https://github.com/GoogleCloudPlatform/gcloud-java/releases) and open the appropriate release draft. Make sure the "Tag Version" is `vX.Y.Z` and the "Release Title" is `X.Y.Z`, where `X.Y.Z` is the release version as listed in the `pom.xml` files.  The draft should already have all changes that impact users since the previous release.  To double check this, you can use the `git log` command and look through the merged master branch pull requests.  Here is an example of the log command to get non-merge commits between v0.0.12 and v0.1.0: