Update documentation for node discovery process

Clarify node joining conditions and requirements.

Author: josevalim

lib/dns_cluster.ex

@@ -2,23 +2,23 @@ defmodule DNSCluster do
   @moduledoc """
   Simple DNS based cluster discovery.
 
-  A DNS query is made every `:interval` milliseconds to discover new ips.
-
   ## Default node discovery
-  Nodes will only be joined if their node basename matches the basename of the current node.
+
+  By default, nodes will only be joined if their node basename matches the basename of the current node.
   For example, if `node()` is `myapp-123@fdaa:1:36c9:a7b:198:c4b1:73c6:1`, it will try to connect
   to every IP from the DNS query with `Node.connect/1`. But this will only work if the remote node
   has the same basename, like `myapp-123@fdaa:1:36c9:a7b:198:c4b1:73c6:2`. If the remote node's
   basename is different, the nodes will not connect.
 
-  ## Specifying remote basenames
   If you want to connect to nodes with different basenames, use a tuple with the basename and query.
   For example, to connect to a node named `remote`, use `{"remote", "remote-app.internal"}`.
 
   ## Multiple queries
+
   Sometimes you might want to cluster apps with different domain names. Just pass a list of queries
   for this. For instance: `["app-one.internal", "app-two.internal", {"other-basename", "other.internal"}]`.
-  Remember, all nodes need to share the same secret cookie to connect successfully.
+  Remember, all nodes need to share the same secret cookie to connect successfully, and their FQDN
+  must be their IP address (either IPv4 or IPv6).
 
   ## Examples