Expanded 'How to Use' in readme

Readme.md

@@ -46,6 +46,13 @@ Finally, load it from the client side code:
 </script>
 ```
 
+The client-side javascript is not a static file, but instead is served through the 
+same port that the socket is listening on. In many configurations, port 80 will already 
+be running a web service and the socket.io listener will have to be moved to another 
+port. If you set (for example) `app.listen(8000);` then your script source will require:
+
+ `<script src="http://localhost:8000/socket.io/socket.io.js"></script>`
+
 For more thorough examples, look at the `examples/` directory.
 
 ## Short recipes