Prepare "cast"script and produce catchy demo for README.md as animated gif or alike

e.g. we have some helpers which we used before
https://github.com/datalad/screencaster

and would be great to generalize... but where is the script you already used @asmacdo for OHBM demo?

Review README.md and the existing helpers in datalad/screencaster, then locate the prior OHBM demo script referenced in the issue. Clarify how the casting workflow should be generalized before implementing it. Done means a reusable cast script and a catchy animated GIF or equivalent are produced for the README.

Written by the indexing model from the issue text.