Configuring a custom domain for your GitHub Pages site
You can customize the domain name of your GitHub Pages site.
GitHub Pages is available in public repositories with GitHub Free, and in public and private repositories with GitHub Pro, GitHub Team, GitHub Enterprise Cloud, and GitHub Enterprise Server. For more information, see "GitHub's products."
About custom domains and GitHub Pages→
GitHub Pages supports using custom domains, or changing the root of your site's URL from the default, like octocat.github.io, to any domain you own.
Managing a custom domain for your GitHub Pages site→
You can set up or update certain DNS records and your repository settings to point the default domain for your GitHub Pages site to a custom domain.
Troubleshooting custom domains and GitHub Pages→
You can check for common errors to resolve issues with custom domains or HTTPS for your GitHub Pages site.