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 reviewscomments– New comments on issues and pull requestsbranches– Created or deleted branchescommits:all– All commits pushed to any branch