add install.sh

copy from https://github.com/thoughtbot/laptop
they dropped Linux support since https://github.com/thoughtbot/laptop/commit/91048f3f96f0d2d14c1106f746dd51c417a26e30
清理 install.sh

 * 现在它只安装一些最基本的软件了，
ruby, rbenv, nodejs, heroku-toolbelt 之类的我还是手动去安装好了，
因为变化太快了，很容易过时
 * 以后会陆续添加一些软件