versioning info (#373)

Signed-off-by: Christian Henkel <[email protected]>

README.md

@@ -39,6 +39,17 @@ Diagnostics messages that are not aggregated can be visualized by [`rqt_runtime_
 - **Iron Irwini** by the [`ros2-iron` branch](https://github.com/ros/diagnostics/tree/ros2-iron)
 - **Jazzy Jalisco** by the [`ros2-jazzy` branch](https://github.com/ros/diagnostics/tree/ros2-jazzy)
 
+# Versioning and Releases
+
+- (__X__.0.0) We use the major version number to indicate a breaking change.
+- (0.__Y__.0) The minor version number is used to differentiate between different ROS distributions:
+  - x.__0__.z: Humble Hawksbill
+  - x.__1__.z: Iron Irwini
+  - x.__2__.z: Jazzy Jalisco
+  - x.__3__.z: Rolling Ridley
+  - Future releases (Kilted Kaiju 05/25) will get x.__3__.z and _Rolling_ will be incremented accordingly.
+- (0.0.__Z__) The patch version number is used for changes in the current ROS distribution that do not affect the API.
+
 # License
 
 The source code is released under a [BSD 3-Clause license](LICENSE).