add info about changed htaccess file

Author: Tobion

UPGRADE-2.2.md

@@ -1,6 +1,12 @@
 UPGRADE FROM 2.1 to 2.2
 =======================
 
+ * The [`web/.htaccess`](https://github.com/symfony/symfony-standard/blob/2.2/web/.htaccess)
+   file has been enhanced substantially to prevent duplicate content with and
+   without `/app.php` in the URI. It also improves functionality when using
+   Apache aliases or when mod_rewrite is not available. So you might want to
+   update your `.htaccess` file as well.
+
  * The ``_internal`` route is not used any more. It should then be removed
    from both your routing and security configurations. A ``fragments`` key has
    been added to the framework configuration and must be specified when ESI or