Update security.rst with new options in Symfony 8.1

Document the introduction of clientHints, prefetchCache, and prerenderCache options in Symfony 8.1.

Author: alamirault

reference/configuration/security.rst

@@ -408,6 +408,7 @@ It's also possible to use ``*`` as a wildcard for all directives:
         };
 
 .. versionadded:: 8.1
+
     The ``clientHints``, ``prefetchCache`` and ``prerenderCache`` options were
     introduced in Symfony 8.1.