minor #20890 [Form] Update embedded.rst (ousmaneNdiaye)

This PR was submitted for the 7.2 branch but it was merged into the 6.4 branch instead.

Discussion
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[Form] Update embedded.rst

Comment added to specify the name of the fil to edit. (As previous examples)

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Commits
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90def24 Update embedded.rst

Author: javiereguiluz

form/embedded.rst

@@ -87,6 +87,7 @@ inside the task form itself. To accomplish this, add a ``category`` field
 to the ``TaskType`` object whose type is an instance of the new ``CategoryType``
 class::
 
+    // src/Form/TaskType.php
     use App\Form\CategoryType;
     use Symfony\Component\Form\FormBuilderInterface;