Clarify that the encrypted param must also be set.

While the encrypted parameter's documentation clearly states that it needs to
be set, if you are focused on the password parameter's documentation, there's
nothing to draw your attention to the fact that encrypted may also need to be
set.
Merge pull request #7399 from SirScott/postgresql_user_doc_touchup

postgresql_user module documentation:  Clarify that the encrypted param must also be set.