Additional build steps required for Mac

[bskendig]

I recommend adding a Mac section to the readme, with these two additional steps that are required to build the binary.

1. brew install pcre
2. sudo ln -s /opt/homebrew/include /usr/local/include

It needs PCRE installed, or it will fail to build; and if you're on a Mac with Apple Silicon then Homebrew is installed in /opt/homebrew but the build looks in /usr/local/include so that directly needs to be symlinked.