Declare usage rules for contributions

[markpasc]

Does it make sense to declare how we can use contributions? Edits are either data, or very short, per the 140 char size limits.

Stack Overflow sites are labelled that user contributions are under cc-wiki (which seems to be just the by-sa license?). That makes sense for copyrightable contributions. If contributors have copyright to their contributions, how should the site be labelled to declare contributions are provided (to us by contributors and by us to readers) under license?

[anildash]

Contributions should just be cc-by-sa, I think. Whatever's most open.

[markpasc]

I added a notice about the cc-by-sa license to the page footer. Let me know if you think we need to note it some other way.