codereview.cfg: add

Missed this when creating the repo.

Change-Id: Ib30ae8c06a0afc8bb0d67a68d4dc716e66f3dbc8
Reviewed-on: https://go-review.googlesource.com/c/xerrors/+/176458
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
1 file changed