[symfony#7204] link to API doc

Author: xabbuh

components/http_foundation.rst

@@ -560,7 +560,8 @@ class, which can make this even easier::
     $response = JsonResponse::fromJsonString('{ "data": 123 }');
 
 .. versionadded:: 3.2
-    The ``JsonResponse::fromJsonString()`` method was added in Symfony 3.2.
+    The :method:`Symfony\\Component\\HttpFoundation\\JsonResponse::fromJsonString`
+    method was added in Symfony 3.2.
 
 The ``JsonResponse`` class sets the ``Content-Type`` header to
 ``application/json`` and encodes your data to JSON when needed.