add reference to typings in code example

Hi,

For people trying this out who might be more familiar with react than typescript, they may run into this when trying the example:

```sh
TS2071: Unable to resolve external module ''react''.
```

This might confuse them and possibly turn them away. I added a reference to the typings for react and react-typed in the code example. I hope this can help clarify that the typescript compiler needs to know these in order to import at compile time.

I hope this helps.

Thanks,
Mike