Add point_cloud_io to required dependencies

[kirilllzaitsev]

Without point_cloud_io, the app cannot read the files with point clouds:

ERROR: cannot launch node of type [point_cloud_io/read]: point_cloud_io
ROS path [0]=/opt/ros/noetic/share/ros
ROS path [1]=/root/catkin_ws/src
ROS path [2]=/opt/ros/noetic/share

[doctorcolossus]

I also noticed this. It's necessary for running the "ground truth" example, but not the underlying library. So in my opinion it should be documented that it's required to run that example, but not made a dependency for the package.