feat(setup): explore automated xcode install

[HipsterBrown]

While working on some separate improvements to this project, I was motivated to do some research into automating the xcode command line tools installation within xs-dev. This led me to the xcode-install gem, which provides a pretty clear process for downloading, extracting, and enabling xcode tooling on behalf of the user.

This is not an immediate need since Apple provides decent documentation and processes themselves for getting xcode; however, it would be an interesting improvement for the first-time user experience or fresh install environment.