crfs: mention that crfs has moved
crfs: mention that crfs has moved

Change-Id: Ifa30ca9f3d0dcdfd533833a0bcffaa0083b19a35
Reviewed-on: https://go-review.googlesource.com/c/build/+/168919
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

golang/build,golang/build,golang/build,golang/build