html/template: Clarifying references to "text/template" in the documentation.
html/template: Clarifying references to "text/template" in the documentation.

Fixes issue 4634.

R=adg, kevlar
CC=golang-dev
https://codereview.appspot.com/7066053
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go