Make it available as a pre-commit hook

Hi,

It would be great if you could make it available as a pre-commit hook.
It needs obviously a .pre-commit-hooks.yaml file, but also the interface
might need some change: only giving warning message,
and exiting with 0 error code in case of no warnings, and non-zero, if there is at least one warning.
Maybe a -w / --warning-only option  would be an easy solution.
