Add list of distros branches to README

Fixes #294

README.md

@@ -2,3 +2,21 @@ ROS 2 examples
 ==============
 
 To see some of these examples in use, visit the ROS 2 Tutorials page: https://index.ros.org/doc/ros2/Tutorials/
+
+Branches
+--------
+
+This repo targets different ROS distributions on different branches.
+You must use the branch matching the ROS distro being used when building from source.
+
+Ony [non-EOL ROS distributions](https://index.ros.org/doc/ros2/Releases/) are supported.
+
+| ROS Distro | Branch   |
+|------------|----------|
+| Rolling    | master   |
+| Foxy       | foxy     |
+| Eloquent   | eloquent |
+| Dashing    | dashing  |
+| Crystal    | crystal  |
+| Bouncy     | bouncy   |
+| Ardent     | ardent   |