Add a note about the NAT setup example.

I think we should keep it with this generic description
which works most of the time.

PR:		docs/33724 (inspired by)
Submitted by:	Saurabh Gupta <saurabh_gupta77 at yhoo dot com>

en_US.ISO8859-1/books/handbook/advanced-networking/chapter.sgml

@@ -3089,6 +3089,12 @@ ISDN BRI line</literallayout>
         to the Internet router, the other connecting to a LAN.  All the
         machines on the LAN are connected through a hub or switch.</para>
 
+      <note>
+	<para>There are many ways to get a LAN connected to the Internet
+	  through a &os; gateway.   This example will only cover a
+	  gateway with at least two NICs.</para>
+      </note>
+
       <mediaobject>
         <imageobject>
           <imagedata fileref="advanced-networking/natd">