added preview only statement

Author: selvasingh

step-04-monitor-java-ee-app/README.md

@@ -170,6 +170,10 @@ az webapp stop -g ${RESOURCE_GROUP} -n ${WEBAPP}
 az webapp start -g ${RESOURCE_GROUP} -n ${WEBAPP}
 ```
 
+>🚧 - __Preview-specific__ downloading, installing and engaging the Application Insights Java
+in-process agent is only necessary while JBoss EAP on App Service is in preview. Soon, the agent
+will be pre-installed and auto-engaged as part of code-less attach feature.
+
 ## Use Java EE application and make few REST API calls
 
 Open the Java EE application running on JBoss EAP in App Service Linux: