Consider including tree in installation

[joelostblom]

I recently found out that there is a conda package on mac os for this, which means that we don't need to mess with homebrew for just getting this single command, which makes it easier to adapt.

I also found that windows users can probably get it in git bash by just downloading an executable and putting it in the right folder, which we could make into a single command. I will need to try it out myself, but this answer suggests it's possible https://superuser.com/a/1353926

Is this command something you think could fit into 521 @flor14 ? I am thinking just a short mention around where we talk about ls `etc.