Readme clean up

[wbalmer]

The readme could use a bit of clean up and nicer presentation. Maybe with some friendly space emojis, better formatting, and some headers.

[gotten]

With the new content of ./tests/ we might need to change the test instructions to:

cd ./tests/
pytest -vvs

or something similar. I'm not too familiar with pytest. This seems to mix the python output with the test results but it allows you to track the fitting step. Perhaps @tomasstolker has an idea of what the best test instructions are for the user?

Edit: these instructions don't seem to show/save the plots, even though it passed the tests. Without the teardown class it keeps the pictures. Otherwise we should reintroduce the example script (which gives a 404 following the instructions and needs some changes anyway because the module is backtracks with s now).

[tomasstolker]

pytest can be used to make sure that nothing breaks in the code. Whenever a PR is now created, it will run the tests now with the Actions workflow. This can also be executed just as pytest from the main folder or indeed from within the tests folder. We can add more specific tests there to check e.g. specific values or if a plot file is created.

As a tutorial for user, I would recommend using sphinx and creating a page on e.g. readthedocs. There we could also include a notebook with the example of HD 131399, installation instructions, etc. I can help set it up if you wish, but @wbalmer would need to create the page on readthedocs.

[gotten]

OK, thank you for the explanation. I'm learning something new every day with this repo :)

[wbalmer]

I can try to learn how to set this up with readthedocs, I do not know sphinx but am happy to learn

[wbalmer]

I cleaned up the readme in commit c8d5206. Our badges look nice and I learned to use rst vs markdown :)