Remove reference to nested middlware in docs

Fixes nextauthjs#5180

docs/docs/tutorials/securing-pages-and-api-routes.md

@@ -42,13 +42,19 @@ export default function Page() {
 
 ### Next.js (Middleware)
 
-With NextAuth.js 4.2.0 and Next.js 12, you can now protect your pages via the middleware pattern more easily. If you would like to protect all pages, you can create a `_middleware.js` file in your root `pages` directory which looks like this.
+With NextAuth.js 4.2.0 and Next.js 12, you can now protect your pages via the middleware pattern more easily. If you would like to protect all pages, you can create a `_middleware.js` file in your root `pages` directory which looks like this:
 
 ```js title="/middleware.js"
 export { default } from "next-auth/middleware"
 ```
 
-Otherwise, if you only want to protect a subset of pages, you could put it in a subdirectory as well, for example in `/pages/admin/_middleware.js` would protect all pages under `/admin`.
+If you only want to secure certain pages, export a `config` object with a `matcher`:
+
+```js
+export { default } from "next-auth/middleware"
+
+export const config = { matcher: ["/dashboard"] }
+```
 
 For the time being, the `withAuth` middleware only supports `"jwt"` as [session strategy](https://next-auth.js.org/configuration/options#session).