Provide brew installation method

[Dentrax]

Summary 💡

It'd be great to have a brew tap for macOS users.

Motivation 🔦

Brew is widely using package manager for macOS. So people directly install without building the source with cargo.

[Byron]

One day when the ein tool is more useful to more people, I think that definitely would be a nice thing to have. It could probably reuse a lot from this implementation here.