Add a Procfile for testing foreman

The foreman run isn't terribly special, but it's another stdio situation
that people get into in real life.

So this is just a way to check that same scenario. For now, no
automation is in place (or necessary?), but it's something to tinker
with via:

    gem install foreman && cd spec && foreman start
Add Pry::Terminal.height! (only used once)