doc: mention reconfiguration design in clustering.md

Documentation/clustering.md

@@ -4,7 +4,7 @@
 
 Starting an etcd cluster statically requires that each member knows another in the cluster. In a number of cases, you might not know the IPs of your cluster members ahead of time. In these cases, you can bootstrap an etcd cluster with the help of a discovery service.
 
-Once an etcd cluster is up and running, adding or removing members is done via [runtime reconfiguration](runtime-configuration.md).
+Once an etcd cluster is up and running, adding or removing members is done via [runtime reconfiguration](runtime-configuration.md). To better understand the design behind runtime reconfiguration, we suggest you read [this](runtime-reconf-design.md).
 
 This guide will cover the following mechanisms for bootstrapping an etcd cluster: