add some comments about unpacking raw data
add some comments about unpacking raw data

vrabaud/velodyne,jpgr87/velodyne,wenjiebit/velodyne,jpgr87/velodyne,wenjiebit/velodyne,niosus/velodyne,niosus/velodyne,pierriko/velodyne,jpgr87/velodyne,wenjiebit/velodyne,lemiant/velodyne,vrabaud/velodyne,davidlandry93/velodyne,davidlandry93/velodyne,niosus/velodyne,davidlandry93/velodyne,lemiant/velodyne,vrabaud/velodyne,lemiant/velodyne,pierriko/velodyne,pierriko/velodyne