move in Z before filament loading: intial version

Firmware/Marlin_main.cpp

@@ -3114,6 +3114,14 @@ void gcode_M701()
 	custom_message = true;
 	custom_message_type = 2;
 
+	if (current_position[Z_AXIS] < 20) {
+	  lcd_setstatuspgm(_T(MSG_PLEASE_WAIT));
+	  current_position[Z_AXIS] += 30;
+	  plan_buffer_line(current_position[X_AXIS], current_position[Y_AXIS], current_position[Z_AXIS], current_position[E_AXIS], 400 / 60, active_extruder); //fast sequence
+	  st_synchronize();
+	  lcd_show_fullscreen_message_and_wait_P(_i("Please insert filament and press the knob."));
+	}
+
 	lcd_setstatuspgm(_T(MSG_LOADING_FILAMENT));
 	current_position[E_AXIS] += 70;
 	plan_buffer_line(current_position[X_AXIS], current_position[Y_AXIS], current_position[Z_AXIS], current_position[E_AXIS], 400 / 60, active_extruder); //fast sequence