Import of Xcode project with Swift

I just purchased OmniGraffle Pro so I could use it to help document class design in Xcode by importing the Xcode project. Since my project is in Swift, there are no Objective-C interface files to process. How will you support this in the future or is there a way I can get my class diagrams drawn other than by hand? I don’t care so much about frameworks, just the core classes of the app design.