Document workaround for the old version of bash that cames with MacOs

[danielo515]

Hello.
I'm setting up devenv in my personal mac (after using it on my work one).
I am getting an "unexpected token ;" error, which I recall it being related to the old version MacOs cames with.
I got some help on discord and a workaround, but I can not recall what was it exactly.
It will be wonderful if you document it somehow in the getting started guide (I think there were two workarounds, one involving nix and direct)