go.tools/README: update to make truthful The old README was misleading, saying the packages were not of interest.
go.tools/README: update to make truthful
The old README was misleading, saying the packages were not of interest.

R=golang-dev, iant
CC=golang-dev
https://codereview.appspot.com/14516051

t-yuki/go.tools.old,t-yuki/go.tools.old,tmc/mirror-go.tools,tmc/mirror-go.tools,t-yuki/go.tools.old,tmc/mirror-go.tools