This idea was rejected in CL 5731059. We should fix the
runtime docs instead.

««« original CL description
cmd/dist: reflect local changes to tree in goversion

runtime.Version() requires a trailing "+" when
tree had local modifications at time of build.

Fixes #7701

LGTM=iant
R=golang-codereviews, iant
CC=golang-codereviews
https://golang.org/cl/84040045

»»»

LGTM=rsc, mra
R=iant, rsc, mra
CC=golang-codereviews
https://golang.org/cl/100520043