Add recma-mdx-displayname to list of plugins

Closes GH-2230.

Reviewed-by: Remco Haszing <remcohaszing@gmail.com>
Reviewed-by: Titus Wormer <tituswormer@gmail.com>

Author: domdomegg

docs/docs/extending-mdx.server.mdx

@@ -5,7 +5,7 @@ export const info = {
     {name: 'Titus Wormer', github: 'wooorm', twitter: 'wooorm'}
   ],
   published: new Date('2021-10-06'),
-  modified: new Date('2021-11-01')
+  modified: new Date('2023-01-18')
 }
 
 # Extending MDX
@@ -68,6 +68,9 @@ You can use this template:
 See also the [list of remark plugins][remark-plugins] and
 [list of rehype plugins][rehype-plugins].
 
+*   [`domdomegg/recma-mdx-displayname`](https://github.com/domdomegg/recma-mdx-displayname)
+    — add a `displayName` to `MDXContent` components, to enable switching
+    on them in production
 *   [`remcohaszing/recma-nextjs-static-props`](https://github.com/remcohaszing/recma-nextjs-static-props)
     — generate [`getStaticProps`](https://nextjs.org/docs/basic-features/data-fetching/get-static-props)
     exposing top level identifiers in Next.js