Rethink current CHANGELOG as Release Notes

The changelog can be automatically generated from the commits at release time.

What would be more interesting instead of maintaining the current changelog at https://github.com/nexB/scancode.io/blob/main/CHANGELOG.rst would be to provide "Release notes" including pertinent information about new features, new pipelines, deprecation, etc...
Similar to Django's release notes https://docs.djangoproject.com/en/5.0/releases/5.0/