update README (#474)
update README (#474)

Signed-off-by: Li <e0860dfb4bd9793d5b078e773d7ccec360dd435c@lyft.com>
cartographer-project/point_cloud_viewer,cartographer-project/point_cloud_viewer,cartographer-project/point_cloud_viewer,cartographer-project/point_cloud_viewer,cartographer-project/point_cloud_viewer