abstract away Homebrew location in README
On MacOS, the default Homebrew prefix changed with the move to arm64. On x86 it was /usr/local, but on arm64 it is /opt/homebrew.
Update the README to find the Homebrew prefix with brew --prefix.
On MacOS, the default Homebrew prefix changed with the move to arm64. On x86 it was /usr/local, but on arm64 it is /opt/homebrew.
Update the README to find the Homebrew prefix with brew --prefix.