There's certainly no readme, that tells you to run the rfdynhud.jar

.
You have to
1. install rfDynHUD to your rFactor folder as usual (as the readme tells you).
2. create a Java project.
3. add the rfdynhud.jar to the Java project's classpath.
4. take the lesson Widgets packages and classes as examples about how to create your own Widgets.