Every repository on GitHub.com comes equipped with a section for hosting documentation, called a wiki. You can use your repository's wiki to share long-form content about your project, such as how to use it, how you designed it, or its core principles. A README file quickly tells what your project can do, while you can use a wiki to provide additional documentation. For more information, see "About READMEs."
With wikis, you can write content just like everywhere else on GitHub. For more information, see "Getting started with writing and formatting on GitHub." We use our open-source Markup library to convert different formats into HTML, so you can choose to write in Markdown or any other supported format.
If you create a wiki in a public repository, the wiki is available to the public. If you create a wiki in a private repository, only people with access to the repository can access the wiki. For more information, see "Setting repository visibility."
You can edit wikis directly on GitHub, or you can edit wiki files locally. By default, only people with write access to your repository can make changes to wikis, although you can allow everyone on GitHub.com to contribute to a wiki in a public repository. For more information, see "Changing access permissions for wikis."
Note: Search engines will not index the contents of wikis. To have your content indexed by search engines, you can use GitHub Pages in a public repository.