Consider setting up Homebrew distribution via a tap

[rnorth]

The installation instructions could be simplified greatly if we use Homebrew for distribution. Per discussions, it would be good to set up a private tap and configure goreleaser to keep it up to date.

We need to ensure that MacOS distribution works without Gatekeeper problems; I don't think that signing/notarizing the binaries should be required for brew installs, but this needs verification.

[sledigabel]

I think it's time to make it an official formula.
Perhaps even github pages.