docs: add information on how to type custom hooks (#22312)

docs/2.guide/3.going-further/2.hooks.md

@@ -42,8 +42,8 @@ App hooks can be mainly used by [Nuxt Plugins](/docs/guide/directory-structure/p
 ```js [plugins/test.ts]
 export default defineNuxtPlugin((nuxtApp) => {
   nuxtApp.hook('page:start', () => {
-      /* your code goes here */
-    })
+    /* your code goes here */
+  })
 })
 ```
 
@@ -73,3 +73,26 @@ export default defineNitroPlugin((nitroApp) => {
 ::alert{icon=👉}
 Learn more about available [Nitro lifecycle hooks](/docs/api/advanced/hooks#nitro-app-hooks-runtime-server-side).
 ::
+
+## Add additional hooks
+
+You can add additional hooks by augmenting the types provided by Nuxt. This can be useful for modules.
+
+```ts
+import { HookResult } from "@nuxt/schema";
+
+declare module '#app' {
+  interface RuntimeNuxtHooks {
+    'your-nuxt-runtime-hook': () => HookResult
+  }
+  interface NuxtHooks {
+    'your-nuxt-hook': () => HookResult
+  }
+}
+
+declare module 'nitropack' {
+  interface NitroRuntimeHooks {
+    'your-nitro-hook': () => void;
+  }
+}
+```