Instructions largely found from here: https://www.esev.com/blog/post/2015-01-pgp-ssh-key-on-yubikey-neo/ https://www.ahrenstein.com/blog/using-a-yubikey-4-and-gpg-for-ssh-on-a-mac/
brew install gnupg2 pinentry-mac
brew install --cask gpg-suite
brew install ykman