docs: add entry for archipel to the apps page

docs/apps.html.in

@@ -67,6 +67,26 @@
       </dd>
     </dl>
 
+    <h2><a name="clientserver">Client/Server applications</a></h2>
+
+    <dl>
+      <dt><a href="http://archipelproject.org">Archipel</a></dt>
+      <dd>
+        Archipel is a libvirt-based solution to manage and supervise virtual
+        machines.  It uses XMPP for all communication. There is no web
+        service or custom protocol.  You just need at least one XMPP server,
+        like eJabberd, to start playing with it.  This allows Archipel to
+        work completely real time.  You never have to refresh the user
+        interface, you'll be notified as soon as something happens. You can
+        even use your favorite chat clients to command your infrastructure.
+      </dd>
+      <dd>
+        Isn't it great to be able to open a chat conversation with your
+        virtual machine and say things like "How are you today?" or "Hey,
+        please reboot"?
+      </dd>
+    </dl>
+
     <h2><a name="desktop">Desktop applications</a></h2>
 
     <dl>