See http://software-carpentry.org/license.html for the licenses covering Software Carpentry material. By contributing you are agreeing that Software Carpentry may redistribute your work under these licenses.
Software Carpentry uses a development workflow similar to that of AstroPy and many other open source projects. The AstroPy docs have excellent sections on:
Text documents should be in Markdown format and compatible with Redcarpet, the engine GitHub uses to render Markdown.
The preferred format for slide presentations is still to be determined.