bug #6439 Fix form/validation directory path (nemo-)

This PR was submitted for the 2.3 branch but it was merged into the 2.7 branch instead (closes #6439).

Discussion
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Fix form/validation directory path

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | 2.3 and higher
| Fixed tickets |

Commits
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3d26303 Fix form/validation directory path

components/form/introduction.rst

@@ -318,9 +318,8 @@ Your integration with the Validation component will look something like this::
     use Symfony\Component\Validator\Validation;
 
     $vendorDir = realpath(__DIR__.'/../vendor');
-    $vendorFormDir = $vendorDir.'/symfony/form/Symfony/Component/Form';
-    $vendorValidatorDir =
-        $vendorDir.'/symfony/validator/Symfony/Component/Validator';
+    $vendorFormDir = $vendorDir.'/symfony/form';
+    $vendorValidatorDir = $vendorDir.'/symfony/validator';
 
     // create the validator - details will vary
     $validator = Validation::createValidator();