add explanation of building with uv to CONTRIBUTING.md

[gvwilson]

Documentation is

• [x] Missing
• [ ] Outdated
• [ ] Confusing
• [ ] Not sure?

Explain in Detail

I am using uv to manage my virtual environment, and would like to add a description of how to do this to CONTRIBUTING.md. In parallel, I expect I would have to modify Makefile to (for example) run uv pip install instead of just pip install.

Your Suggestion for Changes

Should the explanation be interleaved in the way that building with Hatch is interleaved, or should it be a section of its own?