[Documentation] Improve the documentation for pip.ini / pip.config

[eabase]

Description

Please improve the documentation for pip.ini / pip.config.
I cannot find any page or example showing all the available options you can put into those files. Nor description of said.

Expected behavior

• Example file showing all available items you can put into those files.
• Description of each field

Version info

pip version

any

Python version

any

OS

any

How to Reproduce

n/a

Output

No response

Code of Conduct

• [X] I agree to follow the PSF Code of Conduct.