NO-JIRA Update the example for worker service binding

The current example does not work, as it needs a named handler.

src/content/docs/workers/runtime-apis/bindings/service-bindings/index.mdx

@@ -61,6 +61,9 @@ main = "./src/workerB.js"
 import { WorkerEntrypoint } from "cloudflare:workers";
 
 export class WorkerB extends WorkerEntrypoint {
+  // Currently, entrypoints without a named handler are not supported
+  async fetch() { return new Response(null, {status: 404}); }
+
   async add(a, b) { return a + b; }
 }
 ```