Enable automatic anchor generation for headers

[n8henrie]

See also: https://github.com/quicksilver/manual/pull/11#issuecomment-1156402031

[pjrobertson]

In response to this:

Also -- it would be nice to have automatic anchors generated for headers, to be able to link users to specific sections. It looks like we can enable this behavior with a TOC extension in mkdocs: https://www.mkdocs.org/user-guide/writing-your-docs/#linking-to-pages

Fine by me, although the docs are more @skurfer doing than mine so his say is more important.

I'll merge this now so we can move forwards, but if Rob has any suggestions we can come back to this PR.