webhooks: Use append-topic.md for gosquared, greenhouse, hellosign.

zerver/webhooks/gosquared/doc.md

@@ -6,8 +6,7 @@ stream manually even though it's the default.
 
 {!create-bot-construct-url.md!}
 
-To change the topic displayed by the bot, simply append `&topic=name`
-to the end of the above URL, where `name` is your topic.
+{!append-topic.md!}
 
 Go to the account settings page of your GoSquared account and under
 **Project Settings > Services > Webhook > Add New**, add the above

zerver/webhooks/greenhouse/doc.md

@@ -7,13 +7,12 @@ default.
 
 {!create-bot-construct-url.md!}
 
+{!append-topic.md!}
+
 Go to the account settings page of your Greenhouse account and
 under **Webhooks**, add the above URL and name the integration,
 Zulip.
 
-To change the topic displayed by the bot, simply append `&topic=name`
-to the end of the above URL, where `name` is your topic.
-
 {!congrats.md!}
 
 ![](/static/images/integrations/greenhouse/000.png)

zerver/webhooks/hellosign/doc.md

@@ -4,9 +4,7 @@ Configuring the HelloSign integration is easy!
 
 {!create-bot-construct-url.md!}
 
-If you'd like to hardcode the `topic` used by the bot, simply append
-`&topic=topic_name` to the end of the above URL, where `topic_name`
-is your topic.
+{!append-topic.md!}
 
 Go to the account settings page of your HelloSign account and
 under the **Integrations** tab, go to **API** and **Account Callback**.