Add the versionadded directive

Author: javiereguiluz

routing.rst

@@ -778,6 +778,10 @@ URL                       Route          Parameters
     contains a collection of commonly used regular-expression constants such as
     digits, dates and UUIDs which can be used as route parameter requirements.
 
+    .. versionadded:: 6.1
+
+        The ``Requirement`` enum was introduced in Symfony 6.1.
+
 .. tip::
 
     Route requirements (and route paths too) can include