Note default connection string

Author: jmikola

reference/mongodb/mongodb/driver/manager/construct.xml

@@ -50,6 +50,9 @@ mongodb://[username:password@]host1[:port1][,host2[:port2],...[,hostN[:portN]]][
 ]]>
       </programlisting>
      </para>
+     <para>
+      Defaults to <literal>"mongodb://127.0.0.1:27017"<literal> if unspecified.
+     </para>
      <para>
       For details on supported URI options, see
       <link xlink:href="&url.mongodb.docs;reference/connection-string/#connections-connection-options">Connection String Options</link>