Documentation: Elaborate on url and webRoot properties

This is a request for clarifying documentation. I don't understand what problem `url` and/or `webRoot` solve:

> You may want (or need) to debug your application running on a Webserver (especially if it interacts with server-side components like Webservices).

I know when my app needs a running webserver, but I don't understand how these properties relate. I _hoped_ they fired up a web server and served my local frontend files through it. That use case comes up for me all the time, and it's time consuming to have to figure out which web server is the easiest to set up just so I can troubleshoot some HTML/JS's behavior when it's opened locally vs through a server.

I can't tell if that's what this feature does or not. To me, that quote could be interpreted either way. Can the readme include more details about what these properties do and when you need them?

url と webRoot プロパティを説明している README のセクションを読み、既存のドキュメントから各プロパティが何に影響し、Web サーバーを起動するかどうかを確認してください。README を更新し、それらの目的、必要になる場合、ローカルのフロントエンドファイルの提供がサポートされているかどうかを説明してください。

索引モデルが issue の本文から書いたものです。