[docs] show sample packaged data

show previously packaged data, e.g. public neural and behavioral measurements, to give users a sense of what the packaged data should look like.

We have some of this in https://github.com/brain-score/brain-score/blob/master/examples/data.ipynb, perhaps there's a way to combine the two?

Start with examples/data.ipynb and review how it currently presents packaged data. Compare it with the requested public neural and behavioral measurements, then determine how to combine the existing example with a representative packaged-data view. Done means the documentation shows users what packaged data should look like.

Written by the indexing model from the issue text.