kvno invocation correction, language cleanup, afs/cell principal preferred

kvno invocation correction, language cleanup, afs/cell principal preferred

Properly show kvno command syntax, add information about preferring
'afs/cell' for the principal over 'afs', and changed "noted this down"
to "made note of"

Reviewed-on: http://gerrit.openafs.org/4740
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Simon Wilkinson <sxw@inf.ed.ac.uk>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
(cherry picked from commit 07f461e8e35147af605ebc86c139b31d2db0bb28)

Change-Id: If37ab2164a13c6f4b745aaf221337ba56eede043
Reviewed-on: http://gerrit.openafs.org/4793
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>