Update mac instructions
Update mac instructions

darcs-hash:20100321081059-cba2c-adb478c2fbb140533a2b661e529e69d843505142.gz

ardumont/haskell-platform,ardumont/haskell-platform,erantapaa/haskell-platform,erantapaa/haskell-platform,bgamari/haskell-platform,bgamari/haskell-platform,gbaz/haskell-platform,gbaz/haskell-platform,erantapaa/haskell-platform,thomie/haskell-platform