REP 107 update for ROS2

[adamsj-ros]

https://github.com/ros-infrastructure/rep/blob/6d7ef4a13764e88a2fc5da631956a9b398c24793/rep-0107.rst#protocol

Right now the REP states "The default publication rate is 1Hz."

This comment predates ROS2. With ROS2 it would seem more appropriate to use QoS instead of a fixed rate. I suggest the REP be updated to take advantage of ROS2 QoS.