Update readme

Signed-off-by: Addisu Z. Taddese <[email protected]>

README.md

@@ -7,10 +7,14 @@ Foxy | Edifice | [foxy](https://github.com/gazebosim/ros_gz/tree/foxy) | only fr
 Galactic | Edifice | [galactic](https://github.com/gazebosim/ros_gz/tree/galactic) | https://packages.ros.org
 Galactic | Fortress | [galactic](https://github.com/gazebosim/ros_gz/tree/galactic) | only from source
 Humble | Fortress | [humble](https://github.com/gazebosim/ros_gz/tree/humble) | https://packages.ros.org
-Humble | Garden | [humble](https://github.com/gazebosim/ros_gz/tree/humble) | only from source
+Humble | Garden | [humble](https://github.com/gazebosim/ros_gz/tree/humble) | [gazebo packages](https://gazebosim.org/docs/latest/ros_installation#gazebo-garden-with-ros-2-humble-iron-or-rolling-use-with-caution-)[^1]
+Humble | Harmonic | [humble](https://github.com/gazebosim/ros_gz/tree/humble) | only from source
 Rolling | Edifice | [ros2](https://github.com/gazebosim/ros_gz/tree/ros2) | only from source
 Rolling | Fortress | [ros2](https://github.com/gazebosim/ros_gz/tree/ros2) | https://packages.ros.org
 Rolling | Garden | [ros2](https://github.com/gazebosim/ros_gz/tree/ros2) | only from source
+Rolling | Harmonic | [ros2](https://github.com/gazebosim/ros_gz/tree/ros2) | only from source
+
+[^1]: Binaries for these pairings are provided from a the packages.osrfoundation.org repository. Refer to https://gazebosim.org/docs/latest/ros_installation for installation instructions.
 
 For information on ROS 2 and Gazebo compatibility, refer to the [melodic branch README](https://github.com/gazebosim/ros_gz/tree/melodic)