Update ACL help to describe conditions where user is allow to read bucket metadata
Update ACL help to describe conditions where user is allow to read bucket metadata

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