AP_Airspeed: NFC add note about TYPE 0 index

libraries/AP_Airspeed/AP_Airspeed.cpp

@@ -90,7 +90,7 @@ const AP_Param::GroupInfo AP_Airspeed::var_info[] = {
     // @Description: Type of airspeed sensor
     // @Values: 0:None,1:I2C-MS4525D0,2:Analog,3:I2C-MS5525,4:I2C-MS5525 (0x76),5:I2C-MS5525 (0x77),6:I2C-SDP3X,7:I2C-DLVR-5in,8:DroneCAN,9:I2C-DLVR-10in,10:I2C-DLVR-20in,11:I2C-DLVR-30in,12:I2C-DLVR-60in,13:NMEA water speed,14:MSP,15:ASP5033
     // @User: Standard
-    AP_GROUPINFO_FLAGS("_TYPE", 0, AP_Airspeed, param[0].type, ARSPD_DEFAULT_TYPE, AP_PARAM_FLAG_ENABLE),
+    AP_GROUPINFO_FLAGS("_TYPE", 0, AP_Airspeed, param[0].type, ARSPD_DEFAULT_TYPE, AP_PARAM_FLAG_ENABLE),     // NOTE: Index 0 is actually used as index 63 here
 
     // @Param: _DEVID
     // @DisplayName: Airspeed ID