reflect: add a couple of sentences explaining how Methods operate.
reflect: add a couple of sentences explaining how Methods operate.

R=rsc, gri, rsc1, bsiegert
CC=golang-dev
http://codereview.appspot.com/4183053
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go