bug#46700: Update instructions for mac OS installation of emacs via homebrew

[Eli Zaretskii]

> Date: Fri, 26 Feb 2021 14:48:29 +0000
> From: Alan Third <alan@idiocy.org>
> Cc: Tyler Chambers <tyler@iheartapis.com>, 46700@debbugs.gnu.org
> 
> I believe this is purely in reference to the website. I don't have
> any special insight into homebrew, but I see this:
> 
>     breton:/Users/alan>brew cask install emacs
>     Updating Homebrew...
>     [...]
>     Error: Unknown command: cask
> 
> so I guess the requested change is correct.
> 
> I have no idea how to update the website myself.

Thanks.  I think I updated the website, although I don't yet see the
change in my browser.  maybe it takes some time for the changes to
propagate?