Fix more documentation issues

[ZedThree]

Readthedocs is failing again because Sphinx removed the add_stylesheet method that we use to make the equation numbers sensible. To be fair, this method was deprecated since Sphinx 1.8, so I must've missed that when we added it recently.

Also fixes:

• printing the docs location properly
• making sure the Python packages can get picked up properly
• making sure the PDF build works properly (still had issues with this on my machine, but it seems to work ok on RTD)

And also adds a docs top-level target as a synonym for sphinx-html

[ZedThree]

RTD passes again now, so I'm using admin privilege again so we can get this into other PRs