Add Homebrew install steps

[DaniruKun]

I recently created a new Homebrew tap containing a formula for ytarchive: https://github.com/DaniruKun/homebrew-ytarchive

The reason it could not be included in homebrew-core is because of the lack of maintenance from the maintainer + no stable release tag.

[Kethsar]

Put your instructions below 'download' but above 'alternatively' so that the Go related lines stay grouped together. Also revert changing the tabs to spaces in the Usage section of the readme.

[DaniruKun]

@Kethsar done