You can begin using the Minima theme, starting today, by adding
theme: minima to your site's config, a move which eliminates the need to manually copy templates or stylesheets into your repo. While Minima is the only theme supported today, we're working to make more themes available for use on GitHub Pages. Check out the GitHub help documentation for more information on adding a theme to your GitHub Pages site.
This should be a seamless transition for all GitHub Pages users, but if you have a particularly complex Jekyll site, we encourage you to get in touch with us. For more information on these changes, see the Jekyll changelog.