AP_ARHS: add description to AHRS_TRIM parameters

libraries/AP_AHRS/AP_AHRS.cpp

@@ -56,9 +56,21 @@ const AP_Param::GroupInfo AP_AHRS::var_info[] PROGMEM = {
     // @User: Advanced
     AP_GROUPINFO("BARO_USE",  7,    AP_AHRS, _baro_use, 0),
 
-    // @Param: TRIM
-    // @DisplayName: AHRS Trim
-    // @Description: Compensates for the difference between the control board and the frame
+    // @Param: AHRS_TRIM_X
+    // @DisplayName: AHRS Trim Roll
+    // @Description: Compensates for the roll angle difference between the control board and the frame
+    // @Units: Radians
+    // @User: Advanced
+
+    // @Param: AHRS_TRIM_Y
+    // @DisplayName: AHRS Trim Pitch
+    // @Description: Compensates for the pitch angle difference between the control board and the frame
+    // @Units: Radians
+    // @User: Advanced
+
+    // @Param: AHRS_TRIM_Z
+    // @DisplayName: AHRS Trim Yaw
+    // @Description: Not Used
     // @Units: Radians
     // @User: Advanced
     AP_GROUPINFO("TRIM", 8, AP_AHRS, _trim, 0),