Thanks for your interest in contributing! The basic workflow is to fork and send a pull request. Unless you explicitly state otherwise, the act of sending a pull request is a statement that the work is yours (original) and that you provide it under the Creative Commons Attribution License. Note that this is implied by the GitHub Terms of Service.

There is not a mailing list. You should be able to discover work-in-progress (and thus, avoid repeated effort) by searching the issue tracker or the list of currently open pull requests.