[GHC] #9358: Improve flag description in the user guide

[GHC]

#9358: Improve flag description in the user guide
-------------------------------------+-------------------------------------
              Reporter:  jstolarek   |            Owner:  jstolarek
                  Type:  bug         |           Status:  new
              Priority:  normal      |        Milestone:  7.10.1
             Component:              |          Version:  7.8.3
  Documentation                      |         Keywords:
            Resolution:              |     Architecture:  Unknown/Multiple
      Operating System:              |       Difficulty:  Easy (less than 1
  Unknown/Multiple                   |  hour)
       Type of failure:              |       Blocked By:
  Documentation bug                  |  Related Tickets:  #1880
             Test Case:              |
              Blocking:              |
Differential Revisions:  Phab:D444   |
-------------------------------------+-------------------------------------
Changes (by jstolarek):

 * differential:   => Phab:D444


--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9358#comment:20>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler