Fix documentation for setByteArray#
Fix documentation for setByteArray#

The documentation was previously unusably incomplete.

shlevy/ghc,ezyang/ghc,shlevy/ghc,shlevy/ghc,shlevy/ghc,sdiehl/ghc,shlevy/ghc,shlevy/ghc,ezyang/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,ezyang/ghc,ezyang/ghc,shlevy/ghc,ezyang/ghc,sdiehl/ghc,ezyang/ghc,ezyang/ghc,sdiehl/ghc,sdiehl/ghc