1. Check that file out into your Squeak working directory under "release-notes".
2. Open Squeak's Help Browser via Help>ReleaseNotes in the world's main docking bar..
3. Make changes. [CMD]+[5-9] offer interesting formatting options. Text URLs can trigger code evaluation such as "code://String browse".
4. Save changes via [CMD]+[S]. Changes will be written into the file system directly.
5. Upload the changed file into the GitHub repository again. Or ask somebody with access rights to do it.
The call "ReleaseBuilder fileOutChangesBetweenReleases" creates a mark-down file with the latest commit messages. This can be used to track down what happened since the last release.