Add rubocop.yml

[heratyian]

Any thoughts on including a simplified rubocop.yml config here? I find it's been helpful to have it enabled to encourage good style.

[bpurinton]

My concern here is that this template is geared towards beginners, and having them stopped in their tracks by formatting issues while trying to make commits in Phase 1 is not ideal (if the code runs fine as is). Formatting and linting seem more like a Phase 2 skill / aside, and not core content. It seems like that is already in place here: https://learn.firstdraft.com/lessons/390-style ? So perhaps just adding anything there (including a link to a gist with the copyable yml file?)

Nice lesson by the way!