由于某种原因，我无法正确安装rails。 gem install rails说一切都很好，但由于缺少一些gemfile，我无法使用它。我做错了什么？
我正在使用Mac Sierra。
$ ruby -v
ruby 2.4.0p0 (2016-12-24 revision 57164) [x86_64-darwin16]
$ gem install rails
Fetching: rails-5.1.4.gem (100%)
Successfully installed rails-5.1.4
1 gem installed
$ rails -v
Could not locate Gemfile or .bundle/ directory
$ gem list rails
*** LOCAL GEMS ***
jquery-rails (4.3.1)
less-rails (3.0.0, 2.8.0)
rails (5.1.4)
rails-dom-testing (2.0.3, 2.0.2, 2.0.1)
rails-html-sanitizer (1.0.3)
rails_12factor (0.0.3)
rails_serve_static_assets (0.0.5)
rails_stdout_logging (0.0.5)
rspec-rails (3.7.2)
sprockets-rails (3.2.1, 3.2.0)
twitter-bootstrap-rails (4.0.0, 3.2.2)