dmq: docs - note about using same Kamailio version

src/modules/dmq/doc/dmq_admin.xml

@@ -47,6 +47,11 @@
 	Nodes that are not responding to KDMQ reguests are removed the from local
 	list of active nodes, no longer being considered to be part of the KDMQ cluster.
 	</para>
+	<para>
+	IMPORTANT: DMQ must be used only between Kamailio instances having same
+	major version. Internal structures can be incompatible between different
+	major versions and can lead to crashes or unexpected behaviour.
+	</para>
 	<example>
 		<title>KDMQ Request Example</title>
 		<para>