Mark Wikit as deprecated in docs (#692)

With Wikit no longer being actively maintained, its documentation
(in https://wmde.github.io/wikit) should be updated to notify any
readers that Wikit is deprecated and that it has been superseded
by Codex.

Bug: T382052

Author: codders

docs/src/00-doc/01_getting_started.stories.mdx

@@ -2,9 +2,13 @@ import { Meta } from '@storybook/addon-docs/blocks';
 
 <Meta title="Documentation/Getting started" />
 
-# WiKit
+# WiKit (deprecated)
 
-This documents the work on the WiKit product, our Wikidata / Wikibase Design System.
+This documents the deprecated WiKit product, the former Wikidata / Wikibase Design System.
+
+## Deprecation Warning
+
+WiKit **has been deprecated** and will no longer be maintained. For a similar design system and components library for Wikimedia projects, please see [Codex](https://doc.wikimedia.org/codex/latest/).
 
 ## Table of Contents 
 * [Using vue components](#using-vue-components)<br/>