Minor documentation updates

[kodebach]

More update from the review of #2927.

Basics

• Short descriptions should be in the release notes (added as entry in
  doc/news/_preparation_next_release.md which contains _(my name)_)
  Please always add something to the the release notes.
• Longer descriptions should be in documentation or in design decisions.
• Describe details of how you changed the code in commit messages
  (first line should have module: short statement syntax)
• References to issues, e.g. close #X, should be in the commit messages.

Checklist

• I added unit tests for my code
• I fixed all affected documentation
• I added code comments, logging, and assertions as appropriate (see Coding Guidelines)
• I updated all meta data (e.g. README.md of plugins and METADATA.ini)
• I mentioned every code not directly written by me in THIRD-PARTY-LICENSES

Review

Reviewers will usually check the following:

• Documentation is introductory, concise and good to read
• Examples are well chosen and understandable
• Code is conforming to our Coding Guidelines
• APIs are conforming to our Design Guidelines
• Code is consistent to our Design Decisions

[markus2330]

Thank you for creating this PR!