docs: add app:manifest:update hook

docs/3.api/6.advanced/1.hooks.md

@@ -22,6 +22,7 @@ Hook                   | Arguments           | Environment     | Description
 `app:beforeMount`      | `vueApp`            | Client          | Called before mounting the app, called only on client side.
 `app:mounted`          | `vueApp`            | Client          | Called when Vue app is initialized and mounted in browser.
 `app:suspense:resolve` | `appComponent`      | Client          | On [Suspense](https://vuejs.org/guide/built-ins/suspense.html#suspense) resolved event.
+`app:manifest:update`  | `{ id, timestamp }` | Client          | Called when there is a newer version of your app detected.
 `link:prefetch`        | `to`                | Client          | Called when a `<NuxtLink>` is observed to be prefetched.
 `page:start`           | `pageComponent?`    | Client          | Called on [Suspense](https://vuejs.org/guide/built-ins/suspense.html#suspense) pending event.
 `page:finish`          | `pageComponent?`    | Client          | Called on [Suspense](https://vuejs.org/guide/built-ins/suspense.html#suspense) resolved event.