making a note about cluster linking being in preview

cluster-linking/README.md

@@ -3,4 +3,6 @@
 Cluster Linking allows two or more clusters to directly connect at the broker level. It eliminates the need to monitor, secure, and scale 
 another distributed system (e.g. Kafka Connect) to replicate data from one cluster to another--all while preserving offsets to help rationalize about the state of the system.
 
-For information on how to run this demo, please reference the Confluent documentation [here](https://docs.confluent.io/current/multi-dc-deployments/cluster-linking/index.html).
+For information on how to run this demo, please reference the Confluent documentation [here](https://docs.confluent.io/current/multi-dc-deployments/cluster-linking/index.html).
+
+Note: Cluster Linking is currently in preview in CP 6.0.