AP_AHRS: expand description of custom orientation parameters

libraries/AP_AHRS/AP_AHRS.cpp

@@ -115,7 +115,7 @@ const AP_Param::GroupInfo AP_AHRS::var_info[] = {
 
     // @Param: ORIENTATION
     // @DisplayName: Board Orientation
-    // @Description: Overall board orientation relative to the standard orientation for the board type. This rotates the IMU and compass readings to allow the board to be oriented in your vehicle at any 90 or 45 degree angle. The label for each option is specified in the order of rotations for that orientation. This option takes affect on next boot. After changing you will need to re-level your vehicle.
+    // @Description: Overall board orientation relative to the standard orientation for the board type. This rotates the IMU and compass readings to allow the board to be oriented in your vehicle at any 90 or 45 degree angle. The label for each option is specified in the order of rotations for that orientation. This option takes affect on next boot. After changing you will need to re-level your vehicle. Firmware versions 4.2 and prior can use a CUSTOM (100) rotation to set the AHRS_CUSTOM_ROLL/PIT/YAW angles for AHRS orientation. Later versions provide two general custom rotations which can be used, Custom 1 and Custom 2, with CUST_ROT1_ROLL/PIT/YAW or CUST_ROT2_ROLL/PIT/YAW angles.
     // @Values: 0:None,1:Yaw45,2:Yaw90,3:Yaw135,4:Yaw180,5:Yaw225,6:Yaw270,7:Yaw315,8:Roll180,9:Yaw45Roll180,10:Yaw90Roll180,11:Yaw135Roll180,12:Pitch180,13:Yaw225Roll180,14:Yaw270Roll180,15:Yaw315Roll180,16:Roll90,17:Yaw45Roll90,18:Yaw90Roll90,19:Yaw135Roll90,20:Roll270,21:Yaw45Roll270,22:Yaw90Roll270,23:Yaw135Roll270,24:Pitch90,25:Pitch270,26:Yaw90Pitch180,27:Yaw270Pitch180,28:Pitch90Roll90,29:Pitch90Roll180,30:Pitch90Roll270,31:Pitch180Roll90,32:Pitch180Roll270,33:Pitch270Roll90,34:Pitch270Roll180,35:Pitch270Roll270,36:Yaw90Pitch180Roll90,37:Yaw270Roll90,38:Yaw293Pitch68Roll180,39:Pitch315,40:Pitch315Roll90,42:Roll45,43:Roll315,100:Custom 4.1 and older,101:Custom 1,102:Custom 2
     // @User: Advanced
     AP_GROUPINFO("ORIENTATION", 9, AP_AHRS, _board_orientation, 0),