lib/time: update link in README; draft now an RFC
lib/time: update link in README; draft now an RFC

R=golang-dev, minux.ma, bradfitz
CC=golang-dev
https://codereview.appspot.com/7704043
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go