Consider using Raspberry Pi Imager to install from macOS

When we replaced balenaEtcher with Rufus in #20423 (closed), we didn't replace balenaEtcher for macOS.

We explained a bit why in https://tails.net/news/rufus/.

Still, we might document Raspberry Pi Imager instead of balenaEtcher.

The UX is very awkward to install Tails as demonstrated in #20760 (closed), but it wouldn't be difficult to do, especially, now that most of the Ikiwiki mangling has been done already in #20423 (closed).

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information