separate out tested models

[LevanBokeria]

For the PyPI version, we would like only the tested models to be released while all the other ones are on the dev branch available through the repo.

[LevanBokeria]

Hi @MaxBalmus

This branch will be a "release" branch. I've branched off of dev but I'm making changes such that only the tested models and their associated instructions get merged into main to be then published on PyPI.

So I've deleted all the models except the Naghavi model and the KorakianitisMixedModel. In the ModularCirc/Models/README.md file, I've removed description of other models but I've noticed that KorakianitisMixedModel did not actually have a dedicated description. Could you take a look and update that README as you see fit for properly describing the KorakianitisMixedModel?

Furthermore, the main README.md of the repository now has a small description of ModularCirc, followed by installation instructions, and then followed by a small tutorial on how to set up a model. Should that 3rd part go somewhere else? Or do you want that to be part of the main README.md?