This is already documented in the time.Time package
but people might not look there.

Followup to CL 76872, which I submitted accidentally
(Gerrit has placed the Submit button next to Reply again.)

Change-Id: Ibfd6a4da241982d591a8698282a0c15fe9f2e775
Reviewed-on: https://go-review.googlesource.com/77010
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>