Better comment for orIfNotFound.
Better comment for orIfNotFound.

Signed-off-by: Edward Z. Yang <dbd597f5635f432486c5d365e9bb585b3eaa1853@cs.stanford.edu>

sdiehl/ghc,sgillespie/ghc,snoyberg/ghc,snoyberg/ghc,vTurbine/ghc,olsner/ghc,shlevy/ghc,snoyberg/ghc,sgillespie/ghc,snoyberg/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,shlevy/ghc,shlevy/ghc,mettekou/ghc,mettekou/ghc,snoyberg/ghc,vTurbine/ghc,olsner/ghc,shlevy/ghc,mettekou/ghc,snoyberg/ghc,sdiehl/ghc,ezyang/ghc,olsner/ghc,ezyang/ghc,vTurbine/ghc,mettekou/ghc,olsner/ghc,vTurbine/ghc,olsner/ghc,sdiehl/ghc,sgillespie/ghc,vTurbine/ghc,ezyang/ghc,shlevy/ghc,ezyang/ghc,ezyang/ghc,vTurbine/ghc,sgillespie/ghc,vTurbine/ghc,sgillespie/ghc,sgillespie/ghc,mettekou/ghc,shlevy/ghc,shlevy/ghc,snoyberg/ghc,olsner/ghc,mettekou/ghc,olsner/ghc,sdiehl/ghc,mettekou/ghc,ezyang/ghc,ezyang/ghc,sgillespie/ghc