Define missing content directory

Using the editor plugin after this file was updated causes errors. Fixed by re-defining the content directory.

index.php

@@ -1,6 +1,7 @@
 <?php
 
 define('ROOT_DIR', realpath(dirname(__FILE__)) .'/');
+define('CONTENT_DIR', ROOT_DIR .'content-sample/');
 define('CONTENT_EXT', '.md');
 define('LIB_DIR', ROOT_DIR .'lib/');
 define('PLUGINS_DIR', ROOT_DIR .'plugins/');