Hadrian: change GHC.hs to Packages.hs in user-settings.md
This change is in the 3rd para of: Command line arguments:
"Builders such as Ghc ... are defined in src/GHC.hs
"
This change is in the 3rd para of: Command line arguments:
"Builders such as Ghc ... are defined in src/GHC.hs
"