Add note to upgrade.md about new Controller alias

upgrade.md

@@ -5,4 +5,6 @@
 - `composer update`.
 - Replace `public/index.php`, `artisan.php`.
 - Add new `expire_on_close` option to `session` configuration file.
-- Remove call to `redirectIfTrailingSlash` in `bootstrap/start.php` file.
+- Remove call to `redirectIfTrailingSlash` in `bootstrap/start.php` file.
+- Edit `app/config/app.php`; in `aliases` change `'Controller' => 'Illuminate\Routing\Controllers\Controller',`
+  to use `Illuminate\Routing\Controller`