docs: clarify RC termination switch behavior

docs/en/advanced_config/flight_termination.md

@@ -1,6 +1,6 @@
 # Flight Termination Configuration
 
-The _Flight termination_ [failsafe action](../config/safety.md#failsafe-actions) may be triggered by a [safety check](../config/safety.md) (e.g. RC Loss, geofence violation, etc. on any vehicle type or in any flight mode), or by the [Failure Detector](../config/safety.md#failure-detector).
+The _Flight termination_ [failsafe action](../config/safety.md#failsafe-actions) may be triggered by a [safety check](../config/safety.md) (e.g. RC Loss, geofence violation, etc. on any vehicle type or in any flight mode), by the [Failure Detector](../config/safety.md#failure-detector), or manually by toggling a termination switch mapped to an RC channel (see [RC_MAP_TERM_SW](../advanced_config/parameter_reference.md#RC_MAP_TERM_SW)).
 
 ::: info
 Flight termination may also be triggered from a ground station or companion computer using the MAVLink [MAV_CMD_DO_FLIGHTTERMINATION](https://mavlink.io/en/messages/common.html#MAV_CMD_DO_FLIGHTTERMINATION) command.

src/modules/rc_update/params.c

@@ -1442,7 +1442,13 @@ PARAM_DEFINE_INT32(RC_MAP_OFFB_SW, 0);
 PARAM_DEFINE_INT32(RC_MAP_KILL_SW, 0);
 
 /**
- * Termination switch channel
+ * Termination switch channel.
+ *
+ * Use this channel to trigger flight termination. When flight termination is activated,
+ * PX4 disables all controllers and sets all PWM outputs to their failsafe values.
+ *
+ * Note: Flight termination is irreversible—once triggered, it cannot be undone.
+ * This is unlike a kill switch, which can be toggled back. Use with caution.
  *
  * @min 0
  * @max 18