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.