> How do you indicate which code is under which license?

You can apply either of these licenses at your choice, that's how it usually works with MIT/Apache. This is to maximize compatibility with other open source licenses. And thanks for the heads-up, I will fix this too.

> Do you plan to add a CONTRIBUTING.md to instruct those who want to help to understand how to start?

Since there's some interest in this, I'm definitely going to add it!