A contributing guide provides important information to those who are interested in helping you with your project. Without a contributing guide, they might not know what you need help with, how they can get started, or how you like to communicate.
Providing the baseline expectations for a contribution to your project makes it much easier for a new user to contribute to the growth and development of your project.
Like the user facing documentation, the contributing guidelines for every project will be very different. Let's keep our first iteration simple and focus on letting people know our system for labels. Don't worry, we'll talk more about labels after you make these edits.