Usually placed in repository’s root, docs, or .github folder.

• README.md

  You can add a README file to your repository to tell other people why your project is useful, what they can do with your project, and how they can use it.

• CONTRIBUTING.md

  A CONTRIBUTING file communicates how people should contribute to your project.

• LICENCE.md

  Public repositories on GitHub are often used to share open source software. For your repository to truly be open source, you’ll need to license it so that others are free to use, change, and distribute the software.

• CODE_OF_CONDUCT.md

  A CODE_OF_CONDUCT file defines standards for how to engage in a community.

• SECURITY.md

  A SECURITY file gives instructions for how to responsibly report a security vulnerability in your project.

• FUNDING.yml

  A FUNDING file displays a sponsor button in your repository to increase the visibility of funding options for your open source project.

• SUPPORT.md

  A SUPPORT file lets people know about ways to get help with your project.

• CODEOWNERS

  You can use a CODEOWNERS file to define individuals or teams that are responsible for code in a repository.

• CNAME

  Configuration of custom domain for GitHub Pages

• .github/ISSUE_TEMPLATE/config.yml and PULL_REQUEST_TEMPLATE/pr.md

  Issue and pull request templates customize and standardize the information you’d like contributors to include when they open issues and pull requests in your repository.

• .github/workflows/ci.yml

  Workflows are custom automated processes that you can set up in your repository to build, test, package, release…

Other useful files

• CHANGELOG.md
• VISION.md
• CONTRIBUTORS.md or AUTHORS.md

Other project properties

• Project name
• Project description
• Project website
• Project keywords

References

• https://opensource.guide
• https://help.github.com/en/github/building-a-strong-community