Intro video - Ask newcomers to upload their video to their cells' folder

@gabor-boros I've noticed that the newcomers have a separate folder to upload their videos - which means that other newcomers joining after them wouldn't be directed to watch videos from other newcomers, and that someone would have to come and move videos to the right place. This PR instructs newcomers to upload their videos directly to their cell's folder, which makes the process self-sustaining.

Good for you?