Sebastian Wick authored Dec 18, 2023 and Marge Bot committed Jan 03, 2024

Let's try to consolidate our documentation in doc/ in the repo. This
includes some documentation from README.md, the HACKING.md coding style
and the gitlab wiki.

The README.md file now links to all top-level topics (i.e. not reachable
via other topics).

This also includes a few small changes to make things more consistent.

Part-of: <!3465>