Add read the docs

[endast]

This pr adds read the docs to the DeepRVAT repo. The individual readme files have been moved to the docs directory.

The docs will be hosted here: deeprvat.readthedocs.io

We are using sphinx to build the docs with the following plugins:

asphinx-autodoc2 automatically generates API documentation
myst_parser A Sphinx and Docutils extension to parse MyST, a rich and extensible flavour of Markdown for authoring technical and scientific documentation.
sphinx_copybutton adds a little “copy” button to the right of our code blocks

[Marcel-Mueck]

seems legit