integrations: Update GitHub intergation for new configuration UI.

zerver/webhooks/github/doc.md

@@ -6,7 +6,10 @@ Get GitHub notifications in Zulip!
 
 1. {!create-an-incoming-webhook.md!}
 
-1. {!generate-webhook-url-basic.md!}
+1. Decide where to send {{ integration_display_name }} notifications, and
+   [generate the integration URL](/help/generate-integration-url). You'll be
+   able to configure which branches you'll receive notifications from, and
+   whether to exclude notifications from private repositories.
 
 1. On your repository's web page, go to **Settings**. Select **Webhooks**,
    and click **Add webhook**. GitHub may prompt you for your password.
@@ -23,10 +26,6 @@ Get GitHub notifications in Zulip!
 
 {!event-filtering-additional-feature.md!}
 
-### Configuration options
-
-{!git-branches-additional-feature.md!}
-
 ### Related documentation
 
 - [GitHub's webhook events documentation][github-webhook-events]