Add homebrew formula

The source of truth for the homebrew forumla should be in this repo in `package/homebrew/`

Example of another project that does this:
https://github.com/mawww/kakoune/blob/master/contrib/kakoune.rb

Current homebrew formula: https://github.com/Homebrew/homebrew-core/blob/master/Formula/elm-format.rb

Start in package/homebrew/ and compare the requested source-of-truth formula with the linked Kakoune example and the current Homebrew homebrew-core Formula/elm-format.rb. Confirm the formula can be maintained from this repository and that the resulting Homebrew package still installs elm-format correctly.

Written by the indexing model from the issue text.