Add link to 5G kit installation video

There is a video for 5G kit installation: https://www.youtube.com/watch?v=YvAwrNtAK2Q

It should be added to the given documentation page: https://docs.turris.cz/hw/omnia/5g/

There can be something like:

Want to watch the assembly process? Check out our step-by-step video tutorial: Watch the video on YouTube