The release notes for a patch should be included in the patch.
If the following applies to the patch, a release note is required:
Cinder uses reno to generate release notes. Please read the docs for details. In summary, use
$ tox -e venv -- reno new <bug-,bp-,whatever>
Then edit the sample file that was created and push it with your change.
To see the results:
$ git commit # Commit the change because reno scans git log.
$ tox -e releasenotes
Then look at the generated release notes files in releasenotes/build/html in your favorite browser.