AP_BattMonitor: add BLHeli ESC to MONITOR param desc

libraries/AP_BattMonitor/AP_BattMonitor_Params.cpp

@@ -13,7 +13,7 @@ const AP_Param::GroupInfo AP_BattMonitor_Params::var_info[] = {
     // @Param: MONITOR
     // @DisplayName: Battery monitoring
     // @Description: Controls enabling monitoring of the battery's voltage and current
-    // @Values: 0:Disabled,3:Analog Voltage Only,4:Analog Voltage and Current,5:Solo,6:Bebop,7:SMBus-Maxell,8:UAVCAN-BatteryInfo
+    // @Values: 0:Disabled,3:Analog Voltage Only,4:Analog Voltage and Current,5:Solo,6:Bebop,7:SMBus-Maxell,8:UAVCAN-BatteryInfo,9:BLHeli ESC
     // @User: Standard
     // @RebootRequired: True
     AP_GROUPINFO_FLAGS("MONITOR", 1, AP_BattMonitor_Params, _type, BattMonitor_TYPE_NONE, AP_PARAM_FLAG_ENABLE),