Auto-deploy documentation to Github Pages

[techygrrrl]

This PR auto-deploys the docs to gh-pages.

You can see an example deployment here: https://techygrrrl.github.io/tau/

The URL that the official repo would use would be: https://Team-TAU.github.io/tau/ or https://team-tau.github.io/tau/ (depending how URL capitalization works on Github Pages)

In order for this to work, you need to do an initial run of the workflow since the current workflow only runs on deployment to main. See this commit for details on how to enable for your branch: https://github.com/techygrrrl/tau/commit/2277812c8cae343ebecb02f7469723eddfe58ffd

After the initial run, you can proceed.

To set up:

1. Go into the repository settings
2. Go to Pages
3. Set the gh-pages branch as the page for Github Pages to use
4. Choose /root

Here's a screenshot.

[FiniteSingularity]

This looks great! I'm heading out on a trip, but will take a closer look when I get back, and we'll get this merged in ASAP.