Update README.md (#506)
Update README.md (#506)

* Clarify what QoS Settings can be configured via the XML.

This addresses issue: https://github.com/ros2/rmw_fastrtps/issues/500

Signed-off-by: Brian Soe <286d97d7760c2f1837e924945cfe49f4fea3225c@flexiv.com>
Signed-off-by: EduPonz <cd06c2e9cb9b657226976502a1edebf7710250ce@eprosima.com>
ros2/rmw_fastrtps,ros2/rmw_fastrtps,eProsima/ROS-RMW-Fast-RTPS-cpp