ruby2.0 installer 下载
http://dl.bintray.com/oneclick/rubyinstaller/rubyinstaller-2.0.0-p353.exe?direct

报错
ERROR: Error installing rails:
The 'atomic' native gem requires installed build tools.

Please update your PATH to include build tools or download the DevKit
from 'http://rubyinstaller.org/downloads' and follow the instructions
at 'http://github.com/oneclick/rubyinstaller/wiki/Development-Kit'

解决(参考https://github.com/oneclick/rubyinstaller/wiki/Development-Kit)：
到http://rubyinstaller.org/downloads/下载安装(c:/DevKit)：
http://cdn.rubyinstaller.org/archives/devkits/DevKit-mingw64-64-4.7.2-20130224-1432-sfx.exe
下载http://nchc.dl.sourceforge.net/project/sevenzip/7-Zip/9.20/7z920.exe
安装到c:/DevKit


ruby dk.rb init
ruby dk.rb install
gem install rails

（之前装过一次，后来装第二次给忘了，在这里记一笔省大家麻烦）

DONE SUCCESS!