Clarify where changes to gn_to_bp should be submitted

Inspired by https://skia-review.googlesource.com/c/skia/+/478958

Change-Id: I09fc56964350e8aa337ddceafacec4d4dbb9ae40
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/674516
Commit-Queue: Leon Scroggins <scroggo@google.com>
Commit-Queue: Nolan Scobie <nscobie@google.com>
Reviewed-by: Nolan Scobie <nscobie@google.com>
1 file changed