doc: Add -help option to fssync-debug manpages

Change-Id: Id90554b1c56437c62ff9982681ac8a64d4d34948
Reviewed-on: http://gerrit.openafs.org/10395
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>