Merge branch '6.4' into 7.2

* 6.4:
  Minor tweak
  Clarify the code flow a little bit more

Author: javiereguiluz

components/runtime.rst

@@ -36,6 +36,9 @@ So how does this front-controller work? At first, the special
 the component. This file runs the following logic:
 
 #. It instantiates a :class:`Symfony\\Component\\Runtime\\RuntimeInterface`;
+#. The front-controller script (e.g. ``public/index.php``) is included by the
+   runtime, making it run again. Ensure this doesn't produce any side effects
+   in your code;
 #. The callable (returned by ``public/index.php``) is passed to the Runtime, whose job
    is to resolve the arguments (in this example: ``array $context``);
 #. Then, this callable is called to get the application (``App\Kernel``);