minor #9039 [Workflow] feature: update the exemple (Simperfit)

This PR was merged into the master branch.

Discussion
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[Workflow] feature: update the exemple

First fix for #9017 by updating the exemples.

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7161148 feature: update the exemple

Author: javiereguiluz

components/workflow.rst

@@ -70,8 +70,12 @@ are trying to use it with::
     $newsletterWorkflow = ...
 
     $registry = new Registry();
-    $registry->add($blogWorkflow, BlogPost::class);
-    $registry->add($newsletterWorkflow, Newsletter::class);
+    $registry->addWorkflow($blogWorkflow, BlogPost::class);
+    $registry->addWorkflow($newsletterWorkflow, Newsletter::class);
+    
+.. versionadded:: 4.1
+    The ``addWorkflow()`` method was introduced in Symfony 4.1. In previous
+    Symfony versions it was called ``add()``.
 
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