MacOS install instructions - lsusb

[Theodlz]

I noticed while going through the discovery book (that uses a micro:bit controller), that I could not run the lsusb command provided after the setup section. It looks like on MacOS, this bin isn't there by default and also needs to be installed with brew, so this PR adds that command to the MacOS-specific installation steps.

[Theodlz]

I am aware that the section where lsusb is mentioned is flagged as Linux only, but I believe that having lsusb is super useful on MacOS even to just check that you are detecting the micro controller after plugging it in.

[BartMassey]

Thanks! This is especially useful on Mac, I think, where there are often problems getting started.

[eldruin]

Thank you!

[BartMassey]

It would be great if someone with a Mac could also expand the Mac section to look more like the Linux section in terms of setting up and verifying setup of devices. I've filed an issue against

[Theodlz]

@BartMassey I ordered the microbit v2 board and will get it next week. I will very likely open some PRs while I go through the guide, which might take me a few weeks (on vacation right now and traveling, so will get to that at best in a week, at most in 3 weeks).

[BartMassey]

Thanks much! I've filed rust-embedded/discovery-mb2#1 ; please do your review and PRs there, as this edition of the Discovery Book is being deprecated shortly.