Clarify domain meaning for gsutil acl help
Clarify domain meaning for gsutil acl help

dtjackson/gsutil,dimfeld/gsutil,BrandonY/gsutil,chriskuehl/gsutil-debian,GoogleCloudPlatform/gsutil,craigcitro/gsutil,mattdr/gsutil,GoogleCloudPlatform/gsutil,ttiurani/gsutil,fishjord/gsutil