Add a note on source distribution 
Add a note on source distribution 

See #219.
sdiehl/ghc,bgamari/shaking-up-ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,izgzhen/hadrian,sdiehl/ghc,snowleopard/shaking-up-ghc,sdiehl/ghc,snowleopard/hadrian