Update doc to clarify OWNERS requirements

Clarify that owners of seldom-updated third_party directories
must still be committers.

Change-Id: Ie2903288714d549b407194ee8818e225dd0103a1
Reviewed-on: https://chromium-review.googlesource.com/754381
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Aaron Gable <agable@chromium.org>
Cr-Commit-Position: refs/heads/master@{#514543}
1 file changed