Try to handle zip downloads?

[zvecr]

Description

Amount of users downloading qmk_fimware from github as a zip doesnt seem to be decreasing. This PR aims to handle that scenario, guiding users to a working setup.

Something like https://stackoverflow.com/a/31781016 maybe? but handle:

• older commit
• local changes

Also changes to be pulled out...

• allow an empty qmk_firmware folder to init
• run qmk doctor in the correct directory