minor #5940 [Cookbook][ServiceContainer] move filename comment to the top of the code block (xabbuh)

This PR was merged into the 2.8 branch.

Discussion
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[Cookbook][ServiceContainer] move filename comment to the top of the code block

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | 2.8+
| Fixed tickets | #5922

Commits
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d5d68ab move filename comment to the top of the code block

Author: xabbuh

cookbook/service_container/shared.rst

@@ -36,9 +36,9 @@ in your service definition:
 
     .. code-block:: php
 
+        // app/config/services.php
         use Symfony\Component\DependencyInjection\Definition;
 
-        // app/config/services.php
         $definition = new Definition('...');
         $definition->setShared(false);