最近在学习 rails，书上说每个项目的 public 文件夹都会有 Index.html 文件以对应首页。挺奇怪的，我的 public 文件夹里面没有 index.html，这是怎么回事？
In Rails 4 the static index.html file has been removed from the public directory and the functionality has been moved to a dynamic route instead. This means that you no longer have to delete public/index.html every time you start a new Rails application.
A new Rails internal controller Rails::WelcomeController has been introduced to serve the dynamic welcome screen. If your application does not have a root route defined in routes.rb, it will render the rails/welcome#index action instead.