Clarify code standards in the docs

[Ostrzyciel]

In CONTRIBUTING I don't see any mention of code standards or pre-commit checks (which I know are implemented). This should be at least briefly explained there, in particular how to run the pre-commit checks.

[Kaszanas]

Great catch @Ostrzyciel I will go back and see how much of all of this should be implemented.

Could you verify that the implemented pre-commit checks are sane and should be kept for the version that we are working on?

I will document, and I think that pre-commit checks are also triggered with the CI.

[Ostrzyciel]

It's not clear for me what pre-commit checks are there currently :D I didn't dig too deep into this. But, they pass in the CI, so I would consider them "sane".

[Kaszanas]

Solved in #39