dillon1000/react

Fix wording to make it more clear that checkbox (input) supports defaultChecked

Fix some confusion about why `input` would support `defaultChecked` (it's because you can have an input of type checkbox).  This has come up a couple of times (https://github.com/facebook/react/pull/5633, https://github.com/facebook/react/pull/5774) but both those PRs were wrong and it was just easier to fix it myself.