Improve output tree structure documentation readability

@DavidMorin and I had a look at the documentation and found that it was hard to find information in the output tree structure section if the reader did not do a linear read recently.

With a bit of work I could provide a foldable tree (as in emacs) with folders description (samplesselection and co) next to it to prevent the reader from having to jump repeatedly between the tree and the descriptions.