Add pre-commit installation instructions to contributing docs

[tim-schilling]

Our project supports pre-commit, but fails to tell a contributor to actually install it.

[sarahboyce]

I think we have an issue that:

• our pip files and currently deployed version needs python 3.9
• our Readme says we use 3.10
• our pre-commit needs 3.11

Relates to: #200

It's a fairly poor local development experience with the different python versions.
Would love us to prioritize the Python upgrade 👍

[shreyash2002]

Hey @tim-schilling I am currently a beginner in python and django. I would like to contribute to this issue

[tim-schilling]

Excellent, thank you for your help!