[release-branch.go1.3] go.tools/godoc: mention sub-repos and package indexes on packages page

««« CL 128490043 / 99ba754ccda0
go.tools/godoc: mention sub-repos and package indexes on packages page

Also several cosmetic tweaks to the package page.

LGTM=r, bradfitz
R=bradfitz, r
CC=golang-codereviews
https://golang.org/cl/128490043
»»»

TBR=bradfitz
R=bradfitz
CC=golang-codereviews
https://golang.org/cl/127630043
4 files changed