Docs: Make previewing in development easier

[JacobCoffee]

When needing to work on docs, I find the following a little cumbersome

psf-salt$ cd docs
psf-salt/docs$ make html && python -m http.server

It would be nice to have

• hot-reloading (sphinx-autobuild?)
• A Makefile target in the root of the repo so that we could just run make docs-serve or something to only need a oneshot command to get going

[ewdurbin]

I agree that some online option would be a benefit.

As a note, docs can be built with the tox target tox -e docs

[hugovk]

sphinx-autobuild is very handy, we have a make htmllive using it for the devguide, CPython docs and PEPs repos. For example:

https://github.com/python/devguide/blob/main/Makefile