Adopt feature for section context menu on the right

[yarikoptic]

see e.g. how bids has it also with mkdocs material: https://bids-specification.readthedocs.io/en/stable/modality-specific-files/magnetic-resonance-imaging-data.html and now even github has it for viewing .md files:
https://github.com/bids-dandisets/dashboard/blob/main/README.md#bids-dandisets-dashboard