MIT License File Missing

[runningjump]

Hi @developit ! Thanks for putting this thing together, it's a huge help. I see the license is listed as MIT in package.json, but I don't see a license file -- any chance of adding that? I can make a PR if it saves you the trouble!

[runningjump]

I also see now that the source files retain Facebook language about the BSD license, which could be an issue for me. Is that still relevant, given that the original transitiongroup component is now maintained by the community?