cmd/pushback: update deploy instructions

Change-Id: I0e2da21255f547c3e8aa5f48c8bbbe7d060f5dc4
Reviewed-on: https://go-review.googlesource.com/34617
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
2 files changed