Add example project.

[michalchudziak]

We should include example project. Just a simple project to show implementation details.

[sethbattin]

I agree. Using this component is complicated by needing an account key in order for the external service to work correctly. But I would expect that anyone attempting to use the react component is willing to also use the service itself.

There's an example usage here: https://github.com/TrueCar/react-launch-darkly/pull/6. The config file setting launchDarkly.clientId is what would need to be replaced with a user's key. The example also references Helmet, which could be removed.