DOC: Add pre-commit commands to CONTRIBUTING.md

[drbenvincent]

Description

CONTRIBUTING.md links out to the PyMC Python style guide with pre-commit, but it does not include the concrete PyTensor developer commands that match CI.

It would be helpful to add a short section to CONTRIBUTING.md showing contributors how to set up and run pre-commit locally, for example:

pre-commit install
pre-commit run --all-files

This would make it easier for new contributors to reproduce the remote code style checks before opening or updating a PR.

Suggested location

Add a short developer checks section near the existing quick links in CONTRIBUTING.md.

[karlhillx]

Adding pre-commit setup commands to CONTRIBUTING.md. Matches the two commands suggested in the issue.