fix README.md (#469)

* fix README.md

with string 'AsController' does not work

* Update README example to use fully qualified class name

Replaced the short class name with its fully qualified counterpart in the README code example for clarity. This ensures accurate context and prevents potential namespace resolution issues.

Author: raffaelecarelle

README.md

@@ -195,7 +195,7 @@ You can add multiple parameters, the violation will happen when none of them mat
 ```php
 $rules[] = Rule::allClasses()
     ->that(new ResideInOneOfTheseNamespaces('App\Controller'))
-    ->should(new HaveAttribute('AsController'))
+    ->should(new HaveAttribute('Symfony\Component\HttpKernel\Attribute\AsController'))
     ->because('it configures the service container');
 ```