docs: add express.static to the express example

closes #64

README.md

@@ -127,8 +127,12 @@ var serveIndex = require('serve-index')
 var app = express()
 
 // Serve URLs like /ftp/thing as public/ftp/thing
-app.use('/ftp', serveIndex('public/ftp', {'icons': true}))
-app.listen()
+// The express.static serves the file contents
+// The serveIndex is this module serving the directory
+app.use('/ftp', express.static('public/ftp'), serveIndex('public/ftp', {'icons': true}))
+
+// Listen
+app.listen(3000)
 ```
 
 ## License