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

[yarikoptic]

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?

[asmacdo]

https://github.com/asmacdo/duct-datalad-demo