Add documentation on how to use tripleo.sh to tripleo-docs. I think just
an overview will be sufficient. I don't feel like we need to go
overboard here, the script is meant to be developer automation, and self
documenting since it's simple bash. No reason to reproduce the same
commands as documention itself.
Change-Id: I4cbd57a32575e1a442c56ebf825e58cf035e19db
7462df79e1