bpo-24241: Add versionchanged directive to the documentation (#342)

Doc/library/webbrowser.rst

@@ -97,6 +97,9 @@ The following functions are defined:
    :func:`get` with a nonempty argument matching the name of a handler you
    declare.
 
+   .. versionchanged:: 3.7
+      *preferred* keyword-only parameter was added.
+
 A number of browser types are predefined.  This table gives the type names that
 may be passed to the :func:`get` function and the corresponding instantiations
 for the controller classes, all defined in this module.