integration-docs: Update Beeminder for new doc format.

Part of #29592.

zerver/webhooks/beeminder/doc.md

@@ -1,17 +1,27 @@
+# Zulip Beeminder integration
+
 Get Beeminder notifications in Zulip whenever you're going
 to derail from your goal!
 
+{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 Beeminder **Reminders** settings.
 
-1. Set **URL for POST** to the URL constructed above. Click
+1. Set **URL for POST** to the URL generated above. Click
    **Save Changes**.
 
+{end_tabs}
+
 {!congrats.md!}
 
 ![](/static/images/integrations/beeminder/001.png)
+
+### Related documentation
+
+{!webhooks-url-specification.md!}