Include external folders in asciidoctor-gradle-plugin

[rcbandit111]

I have this test project which is using asciidoctor-gradle-plugin: https://github.com/rcbandit111/project-documentation

I notice that when project is compiled folders like images and it's content are included into the compiled pages.
But when I create a folder for example files it's not included into the compiled pages. For some reason it's skipped.
Do you know how I can configure this?