[GHC] #16196: Update README.md to reflect gitlab

[GHC]

#16196: Update README.md to reflect gitlab
-------------------------------------+-------------------------------------
           Reporter:  Iceland_jack   |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.6.3
           Keywords:  newcomer       |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 https://gitlab.haskell.org/ghc/ghc's
 [https://gitlab.haskell.org/ghc/ghc/blob/master/README.md README.md] still
 points to

 > Check out the source code from git
 > {{{
 > $ git clone --recursive git://git.haskell.org/ghc.git
 > }}}

 there are probably other other places that need to be updated, marking as
 *newcomer*

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16196>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler