Found broken `/preparation-for-study/app.comflowy.com` link. Please fix!

この issue には説明がありません。

The issue reports a broken link at the path '/preparation-for-study/app.comflowy.com'. First, locate the file or files in the repository that contain this link, likely in documentation or README files. Search for the string 'app.comflowy.com' or the path segment. Once found, determine the correct URL and update the link. Verify the fix by checking the rendered documentation.

索引モデルが issue の本文から書いたものです。