[commit: ghc] wip/nfs-locking: Update README.md (a5a12ec)

[git at git.haskell.org]

Repository : ssh://git@git.haskell.org/ghc

On branch  : wip/nfs-locking
Link       : http://ghc.haskell.org/trac/ghc/changeset/a5a12ec621ad8461cf80cf91fcbf583919358d70/ghc

>---------------------------------------------------------------

commit a5a12ec621ad8461cf80cf91fcbf583919358d70
Author: Moritz Angermann <moritz.angermann at gmail.com>
Date:   Wed Dec 23 14:59:44 2015 +0800

    Update README.md
    
    Adding missing prerequisites. These are probably installed if you build ghc often or use shake, but if not, these are missing.


>---------------------------------------------------------------

a5a12ec621ad8461cf80cf91fcbf583919358d70
 README.md | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/README.md b/README.md
index 5d87bc4..05e247e 100644
--- a/README.md
+++ b/README.md
@@ -8,6 +8,12 @@ This is supposed to go into the `shake-build` directory of the GHC source tree.
 Trying it
 ---------
 
+Prerequisits
+```
+$ cabal install alex
+$ cabal install shake
+```
+
 On Linux,
 ```
 $ git clone git://git.haskell.org/ghc