macOS-specific vignette

[b-rodrigues]

I feel we should have a macOS-specific vignette, mostly because RStudio is not available for macOS through nixpkgs. I think it would be better for users if there's a vignette with "macOS" in the title so that they're immediately attracted to it :)

In it, we could then explain how they could use Nix; either using another IDE (or the console), or better, using with_nix(). We could then also refer to the vignette you're currently writing @philipp-baumann for more detailed examples. What do you think ?

[philipp-baumann]

#109