Enhance README wrt Usage and License

Author: peterschrammel

README.md

@@ -5,3 +5,15 @@ This repository contains a version of the Java Class Library (`rt.jar`) that can
 be used together with
 [JBMC](https://github.com/diffblue/cbmc/tree/develop/jbmc) to
 model-check Java code that calls the standard library.
+
+## Usage
+
+Put the `core-models.jar` on the classpath of the application that you
+model-check using JBMC, e.g.
+```
+jbmc -cp .:cprover-api.jar:core-models.jar com.examples.MyClass.foo
+```
+
+## License
+
+[OpenJDK GPLv2 + Classpath Exception](https://github.com/openjdk/jdk/blob/master/LICENSE)