Rework the mailing list introductory text. As currently written, the
text suggests a new user post directly to freebsd-questions. The new
text routes them through the new mailing list FAQ and the 'how to get
the best results from freebsd-questions' first; and states that some
mailing lists are more oriented to developers than users, and thus
suggests that they should read the charters before posting.

Reviewed by: trhodes