Merge pull request #98 from freemansoft/master

Add comments to describe when AOP invoked

src/main/java/org/springframework/samples/petclinic/util/CallMonitoringAspect.java

@@ -26,6 +26,8 @@ import org.springframework.util.StopWatch;
 /**
  * Simple aspect that monitors call count and call invocation time. It uses JMX annotations and therefore can be
  * monitored using any JMX console such as the jConsole
+ * 
+ * This is only useful if you use JPA or JDBC.  Spring-data-jpa doesn't have any correctly annotated classes to join on 
  *
  * @author Rob Harrop
  * @author Juergen Hoeller