Add Homebrew instructions to README

[SalvatoreT]

This should be good to go as soon as this PR is approved and merged. Homebrew/homebrew-core#74409

[SalvatoreT]

After you brew update:

❯ brew install ki
==> Downloading http://ghcr.io/v2/homebrew/core/ki/manifests/0.3.3
######################################################################## 100.0%
==> Downloading http://ghcr.io/v2/homebrew/core/ki/blobs/sha256:a6343063d109cbf342ccb89419286d3e83105996d718d818be06cc41874b8e80
==> Downloading from http://pkg-containers-az.githubusercontent.com/ghcr1/blobs/sha256:a6343063d109cbf342ccb89419286d3e83105996d718d818be06cc4
######################################################################## 100.0%
==> Pouring ki--0.3.3.arm64_big_sur.bottle.tar.gz
🍺  /opt/homebrew/Cellar/ki/0.3.3: 6 files, 64MB

And then:

❯ ki
ki-shell 0.3/1.4.32
type :h for help
[0] :q

Bye!

This should close the loop on #58. @asm0dey

[asm0dey]

Awesome work, thank you!