Adding link to the SymfonyCasts Twig tutorial

doc/intro.rst

@@ -23,6 +23,10 @@ Twig is used by many Open-Source projects like Symfony, Drupal8, eZPublish,
 phpBB, Matomo, OroCRM; and many frameworks have support for it as well like
 Slim, Yii, Laravel, and Codeigniter — just to name a few.
 
+.. admonition:: Screencast
+
+    Like to learn from video tutorials? Check out the `SymfonyCasts Twig Tutorial`_!
+
 Prerequisites
 -------------
 
@@ -72,3 +76,5 @@ filesystem loader::
     ]);
 
     echo $twig->render('index.html', ['name' => 'Fabien']);
+
+.. _`SymfonyCasts Twig Tutorial`: https://symfonycasts.com/screencast/twig