Add `pre-commit` hook

[chrisdecker1201]

This is a PR for discussion :).

I was looking for a possibility to introduce some kind of automatically validation of SPDX files inside of a git repository.

I found pre-commit, which could be a solution for my goal. It will execute the pyspdxtools --infile for validation.

Currenty this is working only for one file and only for *.json and not the other possible file-formats, but it's working.

Do you have interest in integrating pre-commit? If so, I think I will try to make this possibel.

[maxhbr]

This is a PR for discussion :).

sorry, that no discussion happened yet.