Updated Python Code Style Guidelines

[Anutrix]

Updated Python Code Style Guidelines to use Black now.

[YuriSizov]

As mentioned in godotengine/godot#40627 this should probably refer to pre-commit hooks instead.

[Anutrix]

Should I add both pre-commit hooks and the manual way like it's done for clang-format?
If so, the text for that would be almost the same as that for clang-format's pre-commit hook section. Keeping this in mind, should we move pre-commit subsections to separate single section addressing both clang-format and black?

[YuriSizov]

I think it should be mentioned in some general contribution workflow guide, if not already. But it is still worthwhile mentioning the particular hook for python in the article about python code style. So what if it's similar to CLang one. That's fine. And yes, it doesn't hurt to mention both way to call it, but in my opinion the hooks are more important as they automate all kinds of checks.

[akien-mga]

Thanks!