Fix doc CS

doc/functions/template_from_string.rst

@@ -22,20 +22,24 @@ any related error message:
 .. note::
 
     The ``template_from_string`` function is not available by default.
-    
-    In Symfony projects, you need to load it in your ``services.yaml``::
+
+    On Symfony projects, you need to load it in your ``services.yaml`` file:
+
+    .. code-block:: yaml
 
         services:
             Twig\Extension\StringLoaderExtension:
 
-    or ``services.php``::
+    or ``services.php`` file::
 
         $services->set(\Twig\Extension\StringLoaderExtension::class);
-    
+
     Otherwise, add the extension explicitly on the Twig environment::
 
+        use Twig\Extension\StringLoaderExtension;
+
         $twig = new \Twig\Environment(...);
-        $twig->addExtension(new \Twig\Extension\StringLoaderExtension());
+        $twig->addExtension(new StringLoaderExtension());
 
 .. note::