XMRIG for macOS

Not sure if you are interested in adding directions for macOS users but if you are, then add something like this:

Install `brew` (https://brew.sh) with this

/usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"

And then install `xmrig` with

brew install xmrig

Update to newest version

brew update

and then

brew upgrade