repository license

[brainwane]

This repository doesn't currently mention that it's under an Open Definition-compliant license. We should add one. I suggest CC-BY-SA (Creative Commons Attribution-ShareAlike). cc @RichardLitt

[RichardLitt]

This repository also doesn't mention that it isn't the live repo - the GitBook doesn't sync to it adequately. I need to manually pull over all of the changes.

CC-BY-SA works for me. I wonder if we should use a CC-BY-SA-NC, but I can't think of an actual use-case where that would be helpful (cc @BenJam). I can add that to the README, here, and note that contributions should be listed as suggestions in issues, not in PRs.