Update FAQs and URMA info on the MET website

[dwfncar]

Two recent met-help questions have pointed out stale content on the MET website:

(1) The FAQ's are very outdated:
http://www.dtcenter.org/met/users/support/faqs/index.php
Update: The work to move the FAQ over to the User's Guide was completed in this pull request: /pull/1867 There is a new issue to complete a detailed review of the FAQ here: /issues/1878

(2) John Raby suggests we update info about the RTMA analysis data and replace it with info about URMA.


   Here's the website:


      http://www.dtcenter.org/met/users/downloads/observation_data.php

(The link in the listed here is invalid - I believe this is the desired link https://dtcenter.org/community-code/metplus/input-data )
   Here's the MET-Help ticket:


      https://rt.rap.ucar.edu/rt/Ticket/Display.html?id=78552


   And here's the relevant text from the ticket:

On the DTC website where you describe gridded analysis products, reference is
made to use of RTMA for gridded observations and the link is provided to
access the RTMA products. Ref the email below from Steven Levine, which says
that the NWS uses the Unrestricted Mesoscale Analysis (URMA) for verification
because it is based on a more complete set of point observations. The RTMA is
more of a "quick look" product for users who can't wait the additional 6 hours
to get the product.

[MET-695] created by johnhg