Add basic files for being an extension

root/ext.php

@@ -0,0 +1,9 @@
+<?php
+
+// this file is not really needed, when empty it can be ommitted
+// however you can override the default methods and add custom
+// installation logic
+
+class phpbb_ext_board3_portal_ext extends phpbb_extension_base
+{
+}