docs: add example of typing custom useFetch errors (#29253)

docs/2.guide/4.recipes/3.custom-usefetch.md

@@ -96,6 +96,28 @@ const { data: modules } = await useAPI('/modules')
 </script>
 ```
 
+If you want to customize the type of any error returned, you can also do so:
+
+```ts
+import type { FetchError } from 'ofetch'
+import type { UseFetchOptions } from 'nuxt/app'
+
+interface CustomError {
+  message: string
+  statusCode: number
+}
+
+export function useAPI<T>(
+  url: string | (() => string),
+  options?: UseFetchOptions<T>,
+) {
+  return useFetch<T, FetchError<CustomError>>(url, {
+    ...options,
+    $fetch: useNuxtApp().$api
+  })
+}
+```
+
 ::note
 This example demonstrates how to use a custom `useFetch`, but the same structure is identical for a custom `useAsyncData`.
 ::