Add more details to the description of the fsid_guid dataset property
6333 ZFS should let the user specify or modify the fsid_guid of a dataset

@@ -590,10 +590,19 @@
        descendent of a filesystem that already has a filesystem_limit does not
        override the ancestor's filesystem_limit, but rather imposes an
        additional limit. This feature must be enabled to be used (see
        zpool-features(5)).
 
+     fsid_guid=value
+       Sets the dataset fsid_guid. The fsid_guid is a 64-bit unsigned integer,
+       used to construct the vfs id when mounting a dataset.  This property
+       should only be set if you need the vfs id to be identical on two
+       systems, for example in a NFS migration scenario.  When the fsid_guid
+       is changed for a file system, the file system and any children that
+       inherit the mountpoint are unmounted, then remounted. If the file
+       system was shared, existing NFS clients will require a remount.
+
      mountpoint=path|none|legacy
        Controls the mount point used for this file system. See the Mount
        Points section for more information on how this property is used.
 
        When the mountpoint property is changed for a file system, the file