gh-pages branch missing?

I see there were [some old PRs targeting the `gh-pages` branch](https://github.com/matplotlib/cmocean/pulls?q=is%3Apr+head%3Agh-pages), but it doesn't appear to exist any more. I also see a [readthedocs page](https://cmocean.readthedocs.io/en/latest/), but it seems mostly empty.

We currently serve https://matplotlib.org/cmocean out of [the `matplotlib.github.com` tree](https://github.com/matplotlib/matplotlib.github.com/tree/main/cmocean), but that seems less-than-ideal for updates, as it's about a 10GB clone.

If you can restore the `gh-pages` branch, then I can change the website to start serving from here, which should be easier for you as the docs would be self-contained on this repo.

Start by reviewing the old PRs targeting the gh-pages branch and the current Read the Docs page. Compare that setup with the cmocean tree in matplotlib.github.com, then determine what is needed to restore a self-contained gh-pages branch. Done means the branch exists and the website can be served from this repository.

Written by the indexing model from the issue text.