[release-branch.go1.1] doc: add a "New packages" section to the 1.1 release notes.

««« CL 9344044 / 880991592ded
doc: add a "New packages" section to the 1.1 release notes.

R=adg, r
CC=golang-dev
https://golang.org/cl/9344044
»»»

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/9386043