fix documentation site to be better/nicer

[ctb]

The docs site is hard to navigate and subdivided badly, in part because of mkdocs and the way it does sections on pages vs different pages (or at least the way I'm using it to do all of that stuff).

Chatting with @camillescott I said:

see https://dib-lab.github.io/genome-grist/#configuring-genome-grist

I’d really like the “Configuring genome grist” on the menu on the left to just go directly to the actual link, https://dib-lab.github.io/genome-grist/configuring/, rather than having it be a section in the document.

and she spaketh in response:

ahh I see what you're talking about -- i think the Franklin docs site
does what you want [1]. config is here [2], most important bits being
the nav:: and theme::features defs. dependencies can be found here [3]
because i've been a bit goblin-mode on this repo and there's no
pyproject.toml / requirements.txt / whatever yet. and of course, the
material theme itself [4] is very well documented.

1. https://ucdavis.github.io/HPCCF-franklin-docs/
2. https://github.com/ucdavis/HPCCF-franklin-docs/blob/main/mkdocs.yml
3. https://github.com/ucdavis/HPCCF-franklin-docs/blob/main/.github/workflows/pages.yml
4. https://squidfunk.github.io/mkdocs-material/