1145320 - document running pulp-manage-db after installation.

https://bugzilla.redhat.com/show_bug.cgi?id=1145320

We reference the platform services in a number of places so it seemed a good idea to make it a separate document and just reference it.
I like keeping the server and consumer docs separate. I'm in favor of keeping the server-related stuff in ``server.rst`` and creating a new one for consumer stuff. That keeps it clear which pieces should be deployed together.