doc: correct implicit ACL permissions volume owner

doc: correct implicit ACL permissions volume owner

OpenAFS changed the behavior of implicit administrator permission
for directory ownership.  In OpenAFS only the volume root directory
owner has implicit administrator permissions and they apply to all
directories in the volume not just those with matching ownership.

Change-Id: I8ca0a8874fe17cf7fc575107bd76efb5dc472b10
Reviewed-on: http://gerrit.openafs.org/6951
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@secure-endpoints.com>
Tested-by: Jeffrey Altman <jaltman@secure-endpoints.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>