doc: document the version subcommand

doc: document the version subcommand

Document the built-in version sub-command which displays
the OpenAFS version string. This sub-command is provided
by the cmd library.

Document the switch style -version option provided by the cmd
library for the initcmd based commands: afsmonitor, scout,
xstat_fs_test, and xstat_cm_test.

Reviewed-on: http://gerrit.openafs.org/11161
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
(cherry picked from commit ed52ea68c661a7428baeddeca2d95972fe3fe618)

Change-Id: Ie7a5194b8c407c8899ae71f168dfbaf5b47a3ae5
Reviewed-on: http://gerrit.openafs.org/12096
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Mark Vitale <mvitale@sinenomine.net>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>