Add zuul from scratch doc

This is just a skeleton for now, and should be expanded, but it
should be correct and up to date for what we expect in the v3
release.

Change-Id: I305200cbfc128cc1bc09e809540a873f60e0fe5c
Co-Authored-By: Leif Madsen <lmadsen@redhat.com>
Co-Authored-By: Monty Taylor <mordred@inaugust.com>
Co-Authored-By: Paul Belanger <pabelanger@redhat.com>
3 files changed