chore(doc): add homebrew instructions for MacOS

[curiositycasualty]

Summary

Adds instructions for installing inso via Homebrew now that Homebrew/homebrew-cask#113376 is merged.

Reason

Making inso easier to install and access!

Testing

N/A

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[curiositycasualty]

This docs change specifically targets the single executable because that is what the homebrew cask installs.
At the time of writing the cask, there were complications with getting a Homebrew cask/formula created using the NPM install route. So the new single-executable route was selected as a lower-friction way to get the CLI installed.

[falondarville]

LGTM, thank you so much Isa!