Make your developer playbook public
What
The developer playbook / style guide / handbook should be somewhere publicly accessible, preferably as a prominent part of the developer-aimed documentation.
Why
Contributors should be able to find the project’s software development style, etc., so that their contributions can match style and avoid revision cycles.
When
From the beginning
As soon as you get started, make the code style and related decisions public. Keep in mind that your developer playbook is a living document, so don’t worry about deciding on every issue. You can always update it as you go. But having a public guide will help contributors understand your project’s style and conventions.