Added pre-commit config

[pfebrer]

With pre-commit changes to versions of the checker tools (e.g. isort and black) or even addition/removal of tools will be easier to track. That is, if this config changes, pre-commit will automatically update the environment when a developer tries to add a new commit. This ensures that everyone is using exactly the same tools, and that they don't forget to run them.

If pre-commit is not set up, this file does nothing.

To set it up:

• Install pre-commit: pip install pre-commit
• Run install on root directory: pre-commit install

[zerothi]

Great, could you add a small comment in CONTRIBUTING.md, great!