Add proper attribution to README

[patcon]

While the gift license doesn't require any sort of attribution or licensing derivative code similarly, it's usually nice to do :)

Part of this might involve forking the gift repo (to draw the proper connections in github's network graph), and rebasing your history on top of the gift history. This will not only make it simpler to pull in new features from gift, but will also preserve history metadata, which I think is a good practice :)