integration-docs: Update Heroku for new doc format.

Part of #29592.

zerver/webhooks/heroku/doc.md

@@ -1,20 +1,31 @@
+# Zulip Heroku integration
+
 Receive notifications in Zulip whenever a new version of an app
 is pushed to Heroku using the Zulip Heroku plugin!
 
+{start_tabs}
+
 1. {!create-channel.md!}
 
 1. {!create-an-incoming-webhook.md!}
 
-1. {!generate-integration-url.md!}
+1. {!generate-webhook-url-basic.md!}
 
-1. Go to your project on Heroku
-   and click the **Resources** tab. Add the **Deploy Hooks** add-on.
-   Select the **HTTP Post Hook** plan, and click **Provision**. Click on
-   the **Deploy Hooks** add-on you just added.
+1. In your project on Heroku, go to the **Resources** tab.
 
-1. Set **URL** to the URL constructed above. Click **Save and Send Test**
+1. Add the **Deploy Hooks** add-on. Select the **HTTP Post Hook** plan,
+   and click **Provision**. Click on the **Deploy Hooks** add-on you
+   just added.
+
+1. Set **URL** to the URL generated above. Click **Save and Send Test**
    to send a test message to your Zulip organization.
 
+{end_tabs}
+
 {!congrats.md!}
 
 ![](/static/images/integrations/heroku/001.png)
+
+### Related documentation
+
+{!webhooks-url-specification.md!}