AP_RCMapper: Added warning to RCMAP_THROTTLE

Warning user that changing RCMAP_Throttle could be dangerous

libraries/AP_RCMapper/AP_RCMapper.cpp

@@ -22,7 +22,7 @@ const AP_Param::GroupInfo RCMapper::var_info[] PROGMEM = {
 
     // @Param: THROTTLE
     // @DisplayName: Throttle channel
-    // @Description: Throttle channel number. This is useful when you have a RC transmitter that can't change the channel order easily. Throttle is normally on channel 3, but you can move it to any channel with this parameter.
+    // @Description: Throttle channel number. This is useful when you have a RC transmitter that can't change the channel order easily. Throttle is normally on channel 3, but you can move it to any channel with this parameter. Warning APM 2.X: Changing the throttle channel could produce unexpected fail-safe results if connection between receiver and on-board PPM Encoder is lost. Disabling on-board PPM Encoder is recommended.
     // @Range: 1 8
     // @Increment: 1
     // @User: Advanced