title: What file uses .md extension and how should I edit them?
body: <p>On GitHub, several projects have <code>README.md</code> files. It seems like a simple format file to express text and pictures. </p>
  
  <p>I guess there is an editor or syntax explanation somewhere.</p>
  
  <p>Where can I find an introduction to <code>.md</code> files?</p>