Improve documentation.
Improve documentation.

See https://github.com/haskell/cabal/issues/3198#issuecomment-190978842.

bennofs/cabal,garetxe/cabal,themoritz/cabal,mydaum/cabal,headprogrammingczar/cabal,Heather/cabal,sopvop/cabal,headprogrammingczar/cabal,sopvop/cabal,thomie/cabal,thomie/cabal,garetxe/cabal,themoritz/cabal,sopvop/cabal,bennofs/cabal,kolmodin/cabal,kolmodin/cabal,mydaum/cabal,gbaz/cabal,gbaz/cabal,themoritz/cabal,Heather/cabal