What file uses .md extension and how should I edit them?

Question

On GitHub, several projects have README.md files. It seems like a simple format file to express text and pictures.

I guess there is an editor or syntax

Answer 1

Github's Atom text editor has a live-preview mode for markdown files.

The keyboard shortcut is CTRL+SHIFT+M.

It can be activated from the editor using the CTRL+SHIFT+M key-binding and is currently enabled for .markdown, .md, .mkd, .mkdown, and .ron files.