docs(*): update docs for local3.deisapp.com, local5.deisapp.com

We've created the convenience records for local3.deisapp.com and
local5.deisapp.com, so local clusters no longer have to manage
DNS whatsoever.

closes #747
Merge pull request #978 from deis/local_dns_docs

docs(*): update docs for local3.deisapp.com, local5.deisapp.com