安装Rails3

1.安装Ruby1.9
2.安装DevKit
  cd <DEVKIT_INSTALL_DIR>
  ruby dk.rb init
  ruby dk.rb install
3.升级RubyGems版本
  gem update --system
4.安装Rails
  gem install rails --no-ri --no-rdoc

安装测试
  新建目录 projects
  cd projects
  rails new demo
  检查依存包
  bundle install
  =>Your bundle is complete! Use `bundle show [gemname]` to see where a bundled gem is installed.
启动服务
  rails server
  => Booting WEBrick
访问
  http://localhost:3000