docs: add OSX (homebrew) installation method
docs: add OSX (homebrew) installation method

@trizen thanks for building a wonderful tool! I've been [maintaining a Homebrew tap](https://github.com/TheKevJames/homebrew-youtube-viewer) for building ``youtube-viewer`` -- figured I'd include the link here in case it helps anyone out.
trizen/youtube-viewer,trizen/youtube-viewer