CarrierWave

Automatically detected.

Your model should look like this:

class Article < ActiveRecord::Base
  mount_uploader :asset, AssetUploader
  # don't forget those if you use :attr_accessible (delete method and form caching method are provided by Carrierwave and used by RailsAdmin)
  attr_accessible :asset, :asset_cache, :remove_asset
end

Field will be detected, and a file upload field will be added to your model's form.

More here