Idea-plugin: define resources folder

Hello,
I start using the idea-plugin in order to configure our numerous projects which have a non-standard directory structure.
Now I need to define additional resource folders. Is that possible and if so, how?
In the example (https://docs.gradle.org/current/dsl/org.gradle.plugins.ide.idea.model.IdeaModule.html) I only see how to configure additional source folders.

Thanks
Jan