State which versions of React you support in the docs

[leanne-tite-jg]

Version

2.0.0

Test Case

http://jsbin.com/sacerobuxi/edit?html,js,output

Steps to reproduce

Expected Behavior

Actual Behavior

[ryanflorence]

Now that peer deps work a bit differently in npm@3, and it seems it's gotten a lot of adoption, we should bring back our peerDep on react in package.json.