Updating docs without pushing a release

[cosenal]

I find it odd and inconvenient that we have to publish a new Mitiq release when what we really want to do is just removing a banner from a website. We don't really want the users to upgrade their package from pypi just because we removed a banner.

Here is a solution by Simon Willison that achieves exactly what we want instead: https://til.simonwillison.net/readthedocs/stable-docs

tl;dr: maintain a stable branch that we can edit manually, but that will also be wiped up at every release and replaced with the content of the release. The docs will be published from that branch instead of the latest tag. All of this handled automatically by GitHub Actions.

@natestemen wdyt?