Add ability to autoproduce documentation/tutorial output listings etc

Inspired by review of

- https://github.com/con/nwb2bids/pull/173/files#diff-701f4aa0e19366927d5b78c879d511d5f7cc52a72e42f0f8c539171611407704R247

with long listings of filetrees.

Especially since examples there are based on synthetic data, we might want here to have those listings auto-generated, either at the level of sphinx rendering or with some external command updating them here and thus being part of the git history (for our own sake of review). Otherwise they could quickly outdate.

I have not looked into best ways to produce them ATM. I know that for https://handbook.datalad.org/ (also in sphinx; https://github.com/datalad-handbook/book) some similar machinery was produced... might be worth checking out as part of the research for the optimal setup.

Start by reviewing the existing Sphinx documentation and the handbook.datalad.org/book machinery referenced in the issue. Compare approaches for generating file-tree listings during rendering or through an external command. Done means the documentation listings are generated from the synthetic examples and can be kept current in the project history.

Written by the indexing model from the issue text.