Added some info on command order.

www/tutorial/nscommands.html

@@ -7,6 +7,7 @@
 <ul>
   <li><a href="#INTRO">Introduction</a>
   <li><a href="#TCL">TCL, NS, and node names</a>
+  <li><a href="#ORDER">Ordering issues</a>
   <li><a href="#HARD">Hardware Commands</a>
   <li><a href="#IP">IP Commands</a>
   <li><a href="#OS">OS Commands</a>
@@ -110,6 +111,15 @@ tb-set-ip-link $node0 $link1 192.0.0.128
 
 <hr>
 
+<a name="ORDER"></a><h3>Ordering Issues</h3>
+
+<p>tb- commands have the same status as all other Tcl and NS commands.
+Thus the order matters not only relative to each other but also
+relative other commands.  One common example of this is that IP
+commands must be issued after the links or lans are created.
+
+<hr>
+
 <a name="HARD"></a><h3>Hardware Commands</h3>
 
 <h4>tb-set-hardware</h4>