Slowdown message: More descriptive and less often

src/platforms/posix/px4_layer/drv_hrt.c

@@ -338,8 +338,8 @@ void	hrt_stop_delay()
 	_delay_interval += delta;
 	_start_delay_time = 0;
 
-	if (delta > 10000) {
-		PX4_INFO("simulator is slow. Delay added: %" PRIu64 " us", delta);
+	if (delta > 100000) {
+		PX4_INFO("Computer load temporarily too high for real-time simulation. (slowdown delay: %" PRIu64 " us)", delta);
 	}
 
 	pthread_mutex_unlock(&_hrt_mutex);