Add a comment about Highspeed Analysis dataset

[mslw]

We are now using the Highspeed Analysis dataset in Module 4 as an example of a nested DataLad dataset in the wild. The exercise is based on retrieving a single file from a subdataset.
It was commented on during the workshop, and I think its worth highlighting in writing: because the dataset comes from an actual research project, it was first hosted locally, then moved to a private GIN repo, then the repo was made public, and an additional copy was made on GitHub. All done by the authors in the course of analysis / review, and thanks to DataLad the data publishing came with a minimal overhead.