CONTIBUTING.md files usually explain to new contributors how to contribute via Github. They can also specify other requirements (e.g. a code style, etc). Here in an example from one of the repos from the World Bank.

For this project, I think you could specify:

1. How to contribute via Github
2. Explain the difference between an issue and a PR.

If you want, I can submit a PR (a suggested change) and we can continue the conversation there.