docs(actuators): add flaps and spoilers from RC

Author: ttechnick

docs/en/config/actuators.md

@@ -175,6 +175,8 @@ The fields are:
 
 #### Flap Scale and Spoiler Scale Configuration
 
+The channel setup of flaps and spoilers is described in [Flaps and Spoiler Control with RC](../payloads/generic_actuator_control.md#flaps-and-spoiler-control-with-rc).
+
 "Flap-control" and "Spoiler-control" are aerodynamic configurations that can either be commanded manually by the pilot (using RC, say), or are set automatically by the controller.
 For example, a pilot or the landing system might engage "Spoiler-control" in order to reduce the airspeed before landing.
 

docs/en/payloads/generic_actuator_control.md

@@ -35,6 +35,15 @@ To map a particular RC channel to an output function `RC AUX n` (and hence it's
 For example, to control an actuator attached to AUX pin 3 (say) you would assign the output function `RC AUX 5` to the output `AUX3`.
 You could then use set the RC channel to control the `AUX3` output using `RC_MAP_AUX5`.
 
+
+### Flaps and Spoiler Control with RC
+
+The preferred method to manually actuate spoilers and flaps is to map an RC switch to an `AUX` output, and then map that AUX output to the flap or spoiler function using [FW_FLAPS_MAN](../advanced_config/parameter_reference.md#FW_FLAPS_MAN) or [FW_SPOILERS_MAN](../advanced_config/parameter_reference.md#FW_SPOILERS_MAN).
+
+Alternatively, you can define a flaps channel directly on the RC using [RC_MAP_FLAPS](../advanced_config/parameter_reference.md#RC_MAP_FLAPS). This channel can also be used to control the spoilers by setting [FW_SPOILERS_MAN](../advanced_config/parameter_reference.md#FW_SPOILERS_MAN) to `Flaps channel`.
+
+> **Note:** This method is deprecated, not recommended for new setups, and will be removed in a future release. Use the AUX-based method instead.
+
 ## Generic Actuator Control in Missions
 
 To use generic actuator control in a mission you must first [configure the outputs that you want to control using MAVLink](#generic-actuator-control-with-mavlink).