Consider using CC0 Public Domain declaration

[ssokolow]

As some jurisdictions don't recognize the right to prematurely put your creation into the public domain, it'd be a good idea to use the Creative Commons CC0 public domain declaration rather than writing your own.

It contains an "If your jurisdiction doesn't allow this, then, instead, I license it to you under equivalent terms" clause.

Otherwise, people in those jurisdictions get the default "All Rights Reserved".

...or, if you don't like that for some reason, there's also The Unlicense as a way to put something in the public domain which GitHub likes enough to list in choosealicense.com's list of more options.