[Docs Tutorial] Add missing python tutorial for Bazel

[Rishab260]

Description

Fixes #27824

Adds missing python tutorial for Bazel.

• Added site/en/python.md : containing the Python first build guide.
• Update _index.yaml with the new python first build guide.

Motivation

There is no official guide for the 'first build' for the Python language. See https://bazel.build/start
This PR adds the Python first build guide using the existing python example in examples/py.

This is my first contribution to this project.

Build API Changes

No

Checklist

• I have added tests for the new use cases (if any).
• I have updated the documentation (if applicable).

Release Notes

RELNOTES: None

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.