Usage guidance: Highlight laptop requirement

[chrysn]

When using the course, presenters should be made aware to include a requirement to BYO laptop (or provide terminals) for running the course.

(Right now we're running an intro with 15pax around, and 1/5th of them just have phones with them).

[aabadie]

Thanks for reporting that issue.

I added a note in the main README: https://github.com/RIOT-OS/riot-course#how-to-use-the-course