minor #16789 [Validator] Doctrine annotations is not required anymore for validator (l-vo)

This PR was merged into the 6.0 branch.

Discussion
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[Validator] Doctrine annotations is not required anymore for validator

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f55ad96 Doctrine annotations is not required anymore for validator

Author: javiereguiluz

validation.rst

@@ -23,8 +23,14 @@ install the validator before using it:
 
 .. code-block:: terminal
 
-    $ composer require symfony/validator doctrine/annotations
+    $ composer require symfony/validator
+    
+If your project still use annotations, ``doctrine/annotations`` is also needed:  
 
+.. code-block:: terminal
+
+    $ composer require doctrine/annotations
+    
 .. note::
 
     If your application doesn't use Symfony Flex, you might need to do some