doc: add video

[raulb]

Description

Looking at https://github.com/psviderski/unregistry this morning, I realized that we could add a link to the video so it's rendered inline for those who don't want to read.

The change can be seen here.

Quick checks

• [x] I have followed the Code Guidelines.
• [x] There is no other pull request for the same update/change.
• [ ] I have written unit tests.
• [x] I have made sure that the PR is of reasonable size and can be easily reviewed.