docs: restructure following diataxis

[gruyaume]

Description

At the moment, the project's README.md serves as our official documentation. Here, we restructure the file so that it follows diataxis standards.

We also adapt the CONTRIBUTING.md to follow the same format with a clear and complete getting started tutorial.

Reference

• https://diataxis.fr/

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• I have added tests that validate the behaviour of the software
• I validated that new and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules