Add information for contributors

[domenicoMuscill0]

Would it be possible to update the github page section How to extend this library (or even just a file in this repository cited in the README) with some practical details about code writing style? I think it would be very useful to explain the workflow to follow in writing code or documentation (for example specifying to always create tests files for the code implemented, use relative imports and add the import to the init file) or even tips for helping the contributor follow the style of code of this library (e.g. using c_f.to_device(embeddings, device=device) instead of standard embeddings.to(device) function, running the tests launched by the .github/workflows folder locally before committing the code). In my opinion these changes could be very useful for not very experienced users that want to contribute anyway like me.