There is more going on in this step than just the definition of one non-default task.

I've realised that the place to, at least initially, grind out the scenarios is in the issues. This is what we do in my day job and there's no reason not to do the same here.

I've added the steps which I think ought to be present to https://github.com/bau-build/bau/issues/31. Note that I've omitted the steps which assert the console output. I think I cargo-culted those assertions across too many tests already. They don't need to be everywhere.