Summary:
Some updates to the issue templates, readme and install.md

Creating an FAQ for installation similar to: https://github.com/facebookresearch/detectron2/blob/master/INSTALL.md#common-installation-issues

Reviewed By: gkioxari

Differential Revision: D21117899

fbshipit-source-id: d287c3a7a99c2e425b4e0cffca55a7b225d79e11