Add note on not using the provided router in production

Author: Minishlink

router.php

@@ -2,6 +2,7 @@
 
 // this is just for the easy bootstrapping of the demo
 // adapted from http://stackoverflow.com/a/38926070
+// DON'T USE IN PRODUCTION, please code your own router or use a framework!
 
 chdir(__DIR__);
 $filePath = realpath('./src/'.ltrim($_SERVER["REQUEST_URI"], '/'));