readthedocs shows warning on homepage

[freemansw1]

It seems that readthedocs is now putting a pesky warning on the documentation pages that are on latest by default (see screenshot). This isn't necessarily a bug, but this is not ideal behavior.

We have a few options on how to fix this. The simplest is to set the documentation page to be on the latest release by default, instead of the latest commit. This would have the additional advantage of us being able to sunset the RC branches for minor version updates, moving main to more similar to what (most) other packages do. We'd still keep it for things like the xarray transition.

Another option, of course, is to change documentation providers/formats. I think that's something we will want to do medium-term anyway, but our current team is very bandwidth limited, so now is not the best time to do that.

Finally, we could do nothing. The warning isn't that annoying.