Add contributing documentation on how to generate docs locally

[tim-schilling]

Going through the Djangonaut Space, we realized that we don't have instructions on how to generate and view the documentation locally. As best as I can tell, it's navigating to the docs/ folder and running make html && open _build/html/index.html:

cd docs/
make html
open _build/html/index.html

I wonder if it's the same on Windows?

[matthiask]

Indeed, we should document that.

I think the easiest way (at least if tox is installed) is:

tox -e docs -- html

(I wonder why the spell check is the default when running the docs environment.)

[tim-schilling]

Ahh, that's nice, thank you. Do we want to use tox in the project root's Makefile?

[matthiask]

I don't really know how the Makefile is used to be honest! I almost never work with it because so much of it assumes that you're in an active virtualenv. That said, I'd certainly prefer it if the Makefile used tox or uv or whatever to do its thing.

[tim-schilling]

Ah, I almost always use the makefile 😅

I'm good with reworking things though as you suggested.