Added -dryrun

Added missing information about -dryrun option

Reviewed-on: http://gerrit.openafs.org/4680
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
(cherry picked from commit 97070b425d4c6e4fa4944160c0e7a6965ebb8e75)

Change-Id: I185f0d76a6c95dcffa01713798a06672e6f9bfa3
Reviewed-on: http://gerrit.openafs.org/9623
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>