OF-1519 add info about firewall

documentation/docs/install-guide.html

@@ -262,6 +262,12 @@ plugins on-demand without impacting Openfire.</p>
 Plugins can be managed inside the Openfire admin console. You can also manually delete a plugin at any time by
 deleting its JAR file (Openfire will automatically remove the plugin from memory and delete it's directory when you
 do so).
+    
+<h2><a name="plugins">Firewall</a></h2>
+    
+Server's administrator should open TCP port 5222 for incoming connections for XMPP clients to be able to connect to Openfire.
+Additionally an administrator can also open TCP 9090 (for http) and TCP 9091 (for https), if there is a need to remotely administrate
+Openfire connecting to its Admin Console. We recommend only using 9091 port as it is an encrypted connection.
 
     </div>