Add information on when the functionality was added.

jpjoao · jpjoao · commit c9750dc50a87 · 2020-04-18T13:44:08.000+01:00
diff --git a/reference/forms/types/options/extra_fields_message.rst.inc b/reference/forms/types/options/extra_fields_message.rst.inc
@@ -9,3 +9,7 @@ placeholder ``{{ extra_fields }}`` can be used to display a comma separated
 list of the submitted extra field names.
 
 This message can be pluralized, see :ref:`formatting pluralized messages <component-translation-pluralization>` for details.
+
+    .. versionadded:: 5.1
+
+    The support for pluralization was introduced in Symfony 5.1.
