Warning when running pip with root privileges (sudo pip install)

Hi! In Fedora and perhaps other linux distributions it is generally ill advised to run pip install with root privileges, as it may interfere with system installed packages. Most use cases would be perfectly satisfied by running pip install --user instead.

I’m preparing a patch for pip in Fedora that will issue a warning to the user when pip installing with root privileges, and I’m wondering if you would be interested in a pull request upstream. I’m not familiar with the Windows and MacOS ecosystems so I’m not sure if they would perhaps benefit from the same treatment.

If there’s an interest, I would try to put a pull request together.