[FR]: Docs for py_venv

### What is the current behavior?

I was reading the docs for `py_venv` and they are basically blank. The attributes are `**kwargs`, without docs.

https://github.com/aspect-build/rules_py/blob/main/docs/venv.md

### Describe the feature

It'd be awesome to have more comprehensive docs likes the one we have for `py_binary`.