Add documentation for multiple dragonfly apps in 1 rails app

[Rik Vanmechelen]

I had to add a second dragonfly app to an existing rails application. 

We set everything up the way we thought it should work, but rails just did not like the urls dragonfly was spitting out. We kept on getting routing errors.

That was until i read the upgrade 0.9 to 1.0 guide, in which you mention the following gem of information:

If you're using more than one Dragonfly app then add a line for each in config/initializers/dragonfly.rb

Rails.application.middleware.use Dragonfly::Middleware, :images
Rails.application.middleware.use Dragonfly::Middleware, :assets

It would be valuable to add this to the configuration section of the documentation.

[Mark Evans]

right - on the "rails" page I guess makes more sense?