Update documentation of DatatypeContexts (#5964)
Update documentation of DatatypeContexts (#5964)

MERGED from commit ac2fbb4f6ce7bf9f0742207e1b974bbd556af85a

ilyasergey/GHC-XAppFix,ilyasergey/GHC-XAppFix,ilyasergey/GHC-XAppFix,ilyasergey/GHC-XAppFix