Docs don't introduce the idea of "models"

[jamesrhester]

(Part of JOSS review)

The documentation contains a top-level entry "all models", but the significance or meaning of a "model" is not described anywhere I could find. A suitable place for this description might be either in "getting started", or perhaps a new top level entry with a brief introduction for developers, if this is developer-specific.

[ml-evs]

Thanks again @jamesrhester, I am addressing this in #912. For now, I have made the "all models" page clearer with a more descriptive link in the README. I think it also makes sense to add some examples under "getting started" as you suggest, I will do this in a separate PR.

[ml-evs]

I should just add that any changes we make to the documentation will not be reflected online at https://optimade.org/optimade-python-tools until we make a release.

[jamesrhester]

Thanks, looks good. Just calling them "data models" cleared it up for me.