simple_form_bootstrap.rb

config.wrappers :bootstrap, :tag => 'div', :class => 'form-group', :error_class => 'has-error' do |b|
  b.use :html5
  b.use :placeholder
  b.use :label
  b.use :input, :wrap_with => { :tag => 'div', :class => 'controls' }
  b.use :error, :wrap_with => { :tag => 'span', :class => 'help-block' }
  b.use :hint,  :wrap_with => { :tag => 'p', :class => 'help-block' }
end
config.form_class = "form-vertical"
config.input_class = "form-control"

terminal

rails g simple_form:install --bootstrap