Software Carpentry is an open source/open access project, and we welcome contributions of all kinds. By contributing, you are agreeing that Software Carpentry may redistribute your work under these licenses. Please see this page for a list of contributors to date.
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.