Note /tf_static uses transient_local in Eloquent (ros2#423)

* Note /tf_static uses transient_local in Eloquent

Follow up from ros2/geometry2#160

* Warn about QoS incompatibility

Author: sloretz

source/Releases/Release-Eloquent-Elusor.rst

@@ -53,6 +53,12 @@ The ``geometry_msgs/msg/Quaternion.msg`` interface now default initializes to a
 
 Here is the pull request for more detail: `https://github.com/ros2/common_interfaces/pull/74 <https://github.com/ros2/common_interfaces/pull/74>`_
 
+Static transform broadcasters and listeners now use QoS durability ``transient_local``` on the ``/tf_static`` topic.
+Similar to the latched setting in ROS 1, static transforms only need to be published once.
+New listeners will receive transforms from all static broadcasters that are alive and have published before.
+All publishers must be updated to use this durability setting or their messages won't be received by transform listeners.
+See this pull request for more detail: `https://github.com/ros2/geometry2/pull/160 <https://github.com/ros2/geometry2/pull/160>`_
+
 rclcpp
 ^^^^^^