Improved transport sniffing docs

Closes #15204

docs/java-api/client.asciidoc

@@ -57,11 +57,23 @@ Client client = TransportClient.builder().settings(settings).build();
 //Add transport addresses and do something with the client...
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-The client allows sniffing the rest of the cluster, which adds data nodes
-into its list of machines to use. In this case, note that the IP addresses
-used will be the ones that the other nodes were started with (the
-"publish" address). In order to enable it, set the
-`client.transport.sniff` to `true`:
+The Transport client comes with a cluster sniffing feature which
+allows it to dynamically add new hosts and remove old ones.
+When sniffing is enabled the the transport client will connect to the nodes in its
+internal node list, which is built via calls to addTransportAddress.
+After this, the client will call the internal cluster state API on those nodes
+to discover available data nodes. The internal node list of the client will
+be replaced with those data nodes only. This list is refreshed every five seconds by default.
+Note that the IP addresses the sniffer connects to are the ones declared as the 'publish'
+address in those node's elasticsearch config.
+
+Keep in mind that list might possibly not include the original node it connected to
+if that node is not a data node. If, for instance, you initially connect to a
+master node, after sniffing no further requests will go to that master node,
+but rather to any data nodes instead. The reason the transport excludes non-data
+nodes is to avoid sending search traffic to master only nodes.
+
+In order to enable sniffing, set `client.transport.sniff` to `true`:
 
 [source,java]
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