舊的 GitHub Notifications (Legacy) 標了 Legacy

新的 GitHub App 說明則有點少，另外 Google 才知道這裡有文件

https://github.com/integrations/slack

這幾項通知預設是關閉，要自己打開

These are disabled by default, and can be enabled with the /github subscribe owner/repo [feature] command:

• reviews – Pull request reviews
• comments – New comments on issues and pull requests
• branches – Created or deleted branches
• commits:all – All commits pushed to any branch