Document using round-robin DNS for discovery (#21810)

* Document using round-robin DNS for discovery

Closes #8427

* Improve wording around round robin DNS

* Included jason's suggestion

docs/reference/modules/network.asciidoc

@@ -31,7 +31,12 @@ Defaults to `_local_`.
 In order to join a cluster, a node needs to know the hostname or IP address of
 at least some of the other nodes in the cluster.  This setting provides the
 initial list of other nodes that this node will try to contact. Accepts IP
-addresses or hostnames.
+addresses or hostnames.  If a hostname lookup resolves to multiple IP
+addresses then each IP address will be used for discovery.
+https://en.wikipedia.org/wiki/Round-robin_DNS[Round robin DNS] -- returning a
+different IP from a list on each lookup -- can be used for discovery; non-
+existent IP addresses will throw exceptions and cause another DNS lookup
+on the next round of pinging (subject to JVM DNS caching).
 +
 Defaults to `["127.0.0.1", "[::1]"]`.