No first build guide is present for Python in https://bazel.build/start

### Page link:

https://bazel.build/start

### Problem description (include actual vs expected text, if applicable):

There is no official guide for the 'first build' for the Python language.

I would be happy to write one as I use bazel on a daily basis to build python code bases.

### Where do you see this issue? (include link to specific section of the page, if applicable)

https://bazel.build/start

### Any other information you'd like to share?

Interested in writing the documentation for first build instructions for Python.

Start at https://bazel.build/start and inspect the existing first-build guides linked from that page. Add an official Python first-build guide following the surrounding documentation structure, then verify that it is linked from the start page and provides complete instructions for building a Python project.

Written by the indexing model from the issue text.