Add post "Setting Up a Development Environment"

Signed-off-by: Don Naegely <naegelyd@gmail.com>
And possibly something like *"... to keep Avocado's and Serrano's own requirements from being installed ..."* and *"... if you wish to update Avocado's and/or Serrano's own requirements, ..."*

Ha, I wish I'd know about `--no-deps` before.