docs: improve the release how-to

Provide more details about:
  - how to choose the new version
  - managing the issues and the milestone

README.md

@@ -87,6 +87,13 @@ Copyright © 2023-present, Bonitasoft S.A.
 
 When all updates have been completed, you are ready to publish a new release.
 
+Decide on the new version depending on the type of changes:
+- Follow [semver](https://semver.org/)
+- Check the new commits since the latest release to determine the type of changes included in the new version. This can be done by:
+  - running locally `git log --oneline <latest-release-tag>..HEAD`
+  - going the [latest GitHub release page](https://github.com/process-analytics/bpmn-visualization-addons/releases/latest) and checking the commits since this release (a link is available just above the release title).
+- Until we release the first major version, bump the minor version if the release contains new features or breaking changes.
+
 Go to the [release workflow](https://github.com/process-analytics/bpmn-visualization-addons/actions/workflows/release.yml) in GitHub Actions and run it by choosing the type of release.
 
 This workflow:
@@ -97,6 +104,7 @@ This workflow:
 Manage Milestone:
 - **Note:** we always put issues related to a version in a Milestone whose name matches the version.
 - Ensure the name of the milestone used for the new release version matches the name of the tag/version that has just been pushed. Renamed it if needed.
+- Verify that all issues related to the upcoming release are attached to the milestone. In particular, check the issues that [do not have a milestone](https://github.com/process-analytics/bpmn-visualization-addons/issues?q=is%3Aissue+is%3Aclosed+no%3Amilestone).
 - Clean this opened milestone if some issues are still opened (move them to a new one or discard milestone from them)
 - Close the milestone