minor #9522 Missing namespace (LordPachelbel)

This PR was merged into the 4.0 branch.

Discussion
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Missing namespace

This tripped me up when I was going through this tutorial until I figured out what the namespace was supposed to be.

Commits
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46252b7 The namespace was missing

Author: javiereguiluz

quick_tour/flex_recipes.rst

@@ -177,6 +177,8 @@ rich API for a ``product`` table? Create a ``Product`` entity and give it the
 
     // src/Entity/Product.php
     // ...
+    
+    namespace App\Entity;
 
     use ApiPlatform\Core\Annotation\ApiResource;
     use Doctrine\ORM\Mapping as ORM;