handbook: clarify that cmd examples use sh syntax

Submitted by:	emaste@
Approved by:	bcr@, carlavilla@
Differential Revision:	https://reviews.freebsd.org/D23851

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

@@ -3957,6 +3957,12 @@ ifconfig_<literal>lagg<replaceable>0</replaceable></literal>="up laggproto failo
 	<filename>/etc/inetd.conf</filename> and
 	<filename>/usr/local/etc/dhcpd.conf</filename>.</para>
 
+      <note>
+       <para>The command examples below assume use of the &man.sh.1; shell.
+       &man.csh.1; and &man.tcsh.1; users will need to start a
+       &man.sh.1; shell or adapt the commands to &man.csh.1; syntax.</para>
+      </note>
+
       <procedure>
 	<step>
 	  <para>Create the root directory which will contain a &os;