rake doc:app

rake aborted!
Don't know how to build task 'README.rdoc'
/home/vagrant/.rvm/gems/ruby-2.1.1/bin/ruby_executable_hooks:15:in `eval'
/home/vagrant/.rvm/gems/ruby-2.1.1/bin/ruby_executable_hooks:15:in `<main>'
Tasks: TOP => doc:app => doc/app/index.html
(See full trace by running task with --trace)

rake foo

bundle exec rake doc:app