readlink -f does not exist in OSX. This an option for the gnu version. Which is installed by homebrew as greadlink. alias readlink="greadlink" seems to get it to run but i have further build issues from there.
meta-darwin enables us to build SDKs which run on OSX, it does not let us run bitbake on OSX unfortunately. There has been talk about making that work but it would require significant effort which we simply don't have the resources for at this time.