integration-docs: Update Hello World for new doc format.

Part of #29592.

zerver/webhooks/helloworld/doc.md

@@ -1,15 +1,19 @@
+# Zulip Hello World integration
+
 Learn how Zulip integrations work with this simple Hello World example!
 
 This webhook is Zulip's official [example
 integration](/api/incoming-webhooks-walkthrough).
 
+{start_tabs}
+
 1. The Hello World webhook will use the `test` channel, which is created
     by default in the Zulip development environment. If you are running
     Zulip in production, you should make sure that this channel exists.
 
 1. {!create-an-incoming-webhook.md!}
 
-1. {!generate-integration-url.md!}
+1. {!generate-webhook-url-basic.md!}
 
 1. To trigger a notification using this example webhook, you can use
     `send_webhook_fixture_message` from a [Zulip development
@@ -28,6 +32,12 @@ integration](/api/incoming-webhooks-walkthrough).
     curl -X POST -H "Content-Type: application/json" -d '{ "featured_title":"Marilyn Monroe", "featured_url":"https://en.wikipedia.org/wiki/Marilyn_Monroe" }' http://localhost:9991/api/v1/external/helloworld\?api_key=abcdefgh&stream=channel%20name;
     ```
 
+{end_tabs}
+
 {!congrats.md!}
 
 ![](/static/images/integrations/helloworld/001.png)
+
+### Related documentation
+
+{!webhooks-url-specification.md!}