record updated intro videos

[elf-pavlik]

We are going to remove links to outdated videos from the README #296
At the same time, we should track the need for recording updated versions. Since we have sample implementations we would like to include demo usage this time.

TODO

• setup demo environment

[elf-pavlik]

#299 notes:

@CxRes: current videos have some issues with syncing audio and slides, when I speed up the video slides don't change, when I skip forward than slide changes.
@justinwb: I will try to reproduce