Prose provides a beautifully simple content authoring environment for CMS-free websites. It’s a web-based interface for managing content on GitHub. Use it to create, edit, and delete files, and save your changes directly to GitHub. Host your website on GitHub Pages for free, or set up your own GitHub webhook server.
Todd atWebs by Todd has written some helpful documentation on using Prose.io, which, though written for a specific set-up, may be helpful.