AC_Fence: add the description of FENCE_ACTION in Rover

libraries/AC_Fence/AC_Fence.cpp

@@ -31,6 +31,7 @@ const AP_Param::GroupInfo AC_Fence::var_info[] = {
     // @DisplayName: Fence Action
     // @Description: What action should be taken when fence is breached
     // @Values{Copter}: 0:Report Only,1:RTL or Land,2:Always Land,3:SmartRTL or RTL or Land,4:Brake or Land
+    // @Values{Rover}: 0:Report Only,1:RTL,2:Hold,3:SmartRTL,4:SmartRTL or Hold
     // @Values: 0:Report Only,1:RTL or Land
     // @User: Standard
     AP_GROUPINFO("ACTION",      2,  AC_Fence,   _action,        AC_FENCE_ACTION_RTL_AND_LAND),