Replace understanding docs with macros

SIDEBAR.ftl.md

@@ -27,5 +27,5 @@ There's more to data integration than what is covered here. You can continue to
 * [REST][u-rest]
 * [JSON][u-json]
 
-[u-rest]: /understanding/REST
-[u-json]: /understanding/JSON
+<@u_rest/>
+<@u_json/>

SIDEBAR.md

@@ -0,0 +1,31 @@
+### Related Resources
+
+There's more to data integration than is covered here. You may want to continue your exploration of Spring messaging and integration with the following
+
+### Getting Started Guides
+
+* [Integrating Data][gs-integration]
+* [Capturing Stream Data][gs-capturing-stream-data]
+* [Messaging with JMS][gs-messaging-jms]
+* [Messaging with RabbitMQ][gs-messaging-rabbitmq]
+* [Messaging with Redis][gs-messaging-redis]
+
+[gs-integration]: /guides/gs/integration/
+[gs-capturing-stream-data]: /guides/gs/capturing-stream-data/
+[gs-messaging-jms]: /guides/gs/messaging-jms/
+[gs-messaging-rabbitmq]: /guides/gs/messaging-rabbitmq/
+[gs-messaging-redis]: /guides/gs/messaging-redis/
+
+### Tutorials
+
+* [Designing and Implementing RESTful Web Services with Spring][tut-rest]
+
+[tut-rest]: /guides/tutorials/rest
+
+### Understanding
+
+* [REST][u-rest]
+* [JSON][u-json]
+
+[u-rest]: /understanding/REST
+[u-json]: /understanding/JSON