DO_FENCE_ENABLE when sent as a command (#2091)

message_definitions/v1.0/common.xml

@@ -1702,7 +1702,13 @@
         <param index="7">Empty</param>
       </entry>
       <entry value="207" name="MAV_CMD_DO_FENCE_ENABLE" hasLocation="false" isDestination="false">
-        <description>Mission command to enable the geofence</description>
+        <description>
+          Enable the geofence.
+          This can be used in a mission or via the command protocol.
+          The persistence/lifetime of the setting is undefined.
+          Depending on flight stack implementation it may persist until superseded, or it may revert to a system default at the end of a mission.
+          Flight stacks typically reset the setting to system defaults on reboot.
+	</description>
         <param index="1" label="Enable" minValue="0" maxValue="2" increment="1">enable? (0=disable, 1=enable, 2=disable_floor_only)</param>
         <param index="2" label="Types" enum="FENCE_TYPE">Fence types to enable or disable as a bitmask. A value of 0 indicates that all fences should be enabled or disabled. This parameter is ignored if param 1 has the value 2</param>
         <param index="3">Empty</param>