ekf2: Update parameter descriptions for air data fusion

src/modules/ekf2/ekf2_params.c

@@ -895,7 +895,9 @@ PARAM_DEFINE_FLOAT(EKF2_EV_POS_Z, 0.0f);
 
 /**
 * Airspeed fusion threshold. A value of zero will deactivate airspeed fusion. Any other positive
-* value will determine the minimum airspeed which will still be fused.
+* value will determine the minimum airspeed which will still be fused. Set to about 90% of the vehicles stall speed.
+* Both airspeed fusion and sideslip fusion must be active for the EKF to continue navigating after loss of GPS.
+* Use EKF2_FUSE_BETA to activate sideslip fusion.
 *
 * @group EKF2
 * @min 0.0
@@ -908,6 +910,8 @@ PARAM_DEFINE_FLOAT(EKF2_ARSP_THR, 0.0f);
 * Boolean determining if synthetic sideslip measurements should fused.
 *
 * A value of 1 indicates that fusion is active
+* Both  sideslip fusion and airspeed fusion must be active for the EKF to continue navigating after loss of GPS.
+* Use EKF2_ARSP_THR to activate airspeed fusion.
 *
 * @group EKF2
 * @boolean