docs: add missing \ for consistency

Author: kenjis

user_guide_src/source/libraries/images/002.php

@@ -1,3 +1,3 @@
 <?php
 
-$image = Config\Services::image('imagick');
+$image = \Config\Services::image('imagick');

user_guide_src/source/testing/controllers/005.php

@@ -1,6 +1,6 @@
 <?php
 
-$config              = new Config\App();
+$config              = new \Config\App();
 $config->appTimezone = 'America/Chicago';
 
 $results = $this->withConfig($config)