gcp: add codereview.cfg
gcp: add codereview.cfg

Change-Id: Ib29d0d5f4cb174e4919f4700c147726601aeec7c
Reviewed-on: https://upspin-review.googlesource.com/11084
Reviewed-by: Rob Pike <4dc7c9ec434ed06502767136789763ec11d2c4b7@golang.org>

upspin/gcp,upspin/gcp