This should be added to the installation section of the docs—I might do that if I get a moment, but anyone can—and personally I think it’d be a good idea to have it on the main page, as an alternative to downloading the binary. Homebrew is so convenient that I’m more willing to try out a new piece of software if it’s available through brew.
One possibility would be to for the “Download” button on http://gohugo.ionot go to the GitHub releases page, but instead to the bottom of the page (“Get Started Today!”) where the multiple installation options could be listed.