Add hatch scripts to build, serve and watch the docs + docs improvements

[jtpio]

A couple of improvements to the docs setup:

• Add hatch script to serve the docs
• Use sphinx-autobuild to watch the docs
• Remove the previous Makefile
• Mention building the docs in CONTRIBUTING.md
• Convert more .rst to .md
• Remove "Background" from the nav bar, add "Changelog" and "FAQ" for visibility:

[jtpio]

Ah, not sure why the rest of the CI does not trigger 🤔

[jtpio]

Ah, it looks like GitHub may have automatically disabled them?

Let's try again.

[jtpio]

check-release passes on #586.

So closing and re-opening a new PR to check if that fixes the checks.