docs: service worker types (#8965)

The additional reference is needed for $service-worker to be properly typed

documentation/docs/30-advanced/40-service-workers.md

@@ -24,6 +24,7 @@ The following example caches the built app and any files in `static` eagerly, an
 
 ```js
 // @errors: 2339
+/// <reference types="@sveltejs/kit" />
 import { build, files, version } from '$service-worker';
 
 // Create a unique cache name for this deployment
@@ -108,21 +109,23 @@ navigator.serviceWorker.register('/service-worker.js', {
 Setting up proper types for service workers requires some manual setup. Inside your `service-worker.js`, add the following to the top of your file:
 
 ```original-js
+/// <reference types="@sveltejs/kit" />
 /// <reference no-default-lib="true"/>
 /// <reference lib="esnext" />
 /// <reference lib="webworker" />
 
 const sw = /** @type {ServiceWorkerGlobalScope} */ (/** @type {unknown} */ (self));
 ```
 ```generated-ts
+/// <reference types="@sveltejs/kit" />
 /// <reference no-default-lib="true"/>
 /// <reference lib="esnext" />
 /// <reference lib="webworker" />
 
 const sw = self as unknown as ServiceWorkerGlobalScope;
 ```
 
-This disables access to DOM typings like `HTMLElement` which are not available inside a service worker and instantiates the correct globals. The reassignment of `self` to `sw` allows you to type cast it in the process (there are a couple of ways to do this, but the easiest that requires no additional files). Use `sw` instead of `self` in the rest of the file.
+This disables access to DOM typings like `HTMLElement` which are not available inside a service worker and instantiates the correct globals. The reassignment of `self` to `sw` allows you to type cast it in the process (there are a couple of ways to do this, but the easiest that requires no additional files). Use `sw` instead of `self` in the rest of the file. The reference to the SvelteKit types ensures that the `$service-worker` import has proper type definitions.
 
 ## Other solutions