Suggestion: Support private PyPI servers

[Liam-Deacon]

It would be great if pyroma could look up other PyPI servers defined with $PIP_EXTRA_INDEX_URL environment varaible or in the pip.conf/pip.ini for the user's platform.

[regebro]

Looking at this, pip gathers information from many places, and has different filenames for Windows, etc.
Replicating that is likely a never ending work of tweaking things so that it behaves exactly like pip in all cases, and I definitely do not have the time for that.

So I think we need a different option here. Likely just a parameter for posting the URL to the index in question.