The "About code owners" page does mention that you can define code owners in public repositories with GitHub Free and GitHub Free for organizations, and in public and private repositories with GitHub Pro, GitHub Team, GitHub Enterprise Cloud, and GitHub Enterprise Server.
When the code owner is a team, that team must be visible and it must have write permissions, even if all the individual members of the team already have write permissions directly, through organization membership, or through another team membership.
CODEOWNERS
file location
To use a CODEOWNERS
file, create a new file called CODEOWNERS
in the root, docs/
, or .github/
directory of the repository, in the branch where you'd like to add the code owners.
Each CODEOWNERS
file assigns the code owners for a single branch in the repository. Thus, you can assign different code owners for different branches, such as @octo-org/codeowners-team for a code base on the default branch and @octocat for a GitHub Pages site on the gh-pages branch.