manual control setpoint: add comment about sign

src/modules/uORB/topics/manual_control_setpoint.h

@@ -71,13 +71,20 @@ struct manual_control_setpoint_s {
 	 * the MANUAL_CONTROL mavlink message is defined from -1000 to 1000)
 	 */
 	float x;			/**< stick position in x direction -1..1
-					  in general corresponds to forward/back motion or pitch of vehicle */
+					  in general corresponds to forward/back motion or pitch of vehicle,
+					  in general a positive value means forward or negative pitch and
+					  a negative value means backward or positive pitch */
 	float y;			/**< stick position in y direction -1..1
-					  in general corresponds to right/left motion or roll of vehicle */
+					  in general corresponds to right/left motion or roll of vehicle,
+					  in general a positive value means right or positive roll and
+					  a negative value means left or negative roll */
 	float z;			/**< throttle stick position 0..1
-					  in general corresponds to up/down motion or thrust of vehicle */
+					  in general corresponds to up/down motion or thrust of vehicle,
+					  in general the value corresponds to the demanded throttle by the user,
+					  if the input is used for setting the setpoint of a vertical position
+					  controller any value > 0.5 means up and any value < 0.5 means down */
 	float r;			/**< yaw stick/twist positon, -1..1
-					  in general corresponds to rotation around the vertical
+					  in general corresponds to the righthand rotation around the vertical
 					  (downwards) axis of the vehicle */
 	float flaps;			/**< flap position */
 	float aux1;			/**< default function: camera yaw / azimuth */