Release notes workflow

[kdberends]

Issue

Currently release notes are maintained on the "releases" tab and in docs/Changelog.md. However, our users are used to "release notes" and PDF documents.

Proposed fix

1. Rename "docs/CHANGELOG.MD" to "release_notes.md"
2. update mkdocs.yml to reflect this change in file name
3. Edit Github CI workflow to compile release_notes.md to PDF (e.g. using a pandoc action).

[JacoStout]

I (Jaco) would like to follow D-HYDRO Release notes:

• a cover (Dutch Delta Systems)
• an Introduction with
  ** Release contents (standard text / description of "What FM2prof is") and
  ** Documentation list
• followed by Release summary (a dump of the CHANGELOG.md)

[JacoStout]

I (Jaco) have a cover for the Rel.Notes (attached)
FM2prof-RN.pdf

[rhutten]

@JacoStout, Could you further elaborate on "an Introduction with" ? Are there already markdown files with "What is FM2prof"? And what do you want to include in the documentation list?