Add a pre-commit config file
and document it briefly in the README file.
This comes with a few checkers:
- flake8
- trailing-whitespace
- check-json
- check-yaml
- codespell
Also include commented checkers:
- black: disabled since we are not ready for this yet,
- pydocstyle: disabled since we have way too many pydoctyle errors for now...
See https://pre-commit.com/ for more details.
Related to T1881.