Project timeline, update frequency, what you accept, what you don't etc.
Mention details about what the prerequisites are.
If your project requires a specific branching format to avoid confusion and maintain tracking, provide necessary details.
How to make a pull request, details that you would need from the requestor to understand the PR better. Please provide all the required details and format so that the PRs are created as expected.
If you have a PR template, update it here.