go.text/transform: improve comments based on review of https://golang.org/cl/10538043.
go.text/transform: improve comments based on review of
https://golang.org/cl/10538043.

R=r, mpvl
CC=golang-dev
https://golang.org/cl/10996043

cmars/tools,cmars/tools,golang/text,cmars/tools,cmars/tools,npchp110/text