add comments on config validation
add comments on config validation

xlqian/navitia,Tisseo/navitia,xlqian/navitia,kinnou02/navitia,pbougue/navitia,CanalTP/navitia,xlqian/navitia,pbougue/navitia,Tisseo/navitia,Tisseo/navitia,pbougue/navitia,CanalTP/navitia,CanalTP/navitia,xlqian/navitia,CanalTP/navitia,Tisseo/navitia,patochectp/navitia,patochectp/navitia,patochectp/navitia,CanalTP/navitia,xlqian/navitia,Tisseo/navitia,kinnou02/navitia,kinnou02/navitia,patochectp/navitia,kinnou02/navitia,pbougue/navitia