Update in-app README so that routes work as expected

[simonkotwicz]

closes #133

[eli-darkly]

Thanks. Until you submitted this, I had completely forgotten that adding a path prefix of /relay was something that was in our example code, and not just something you had decided to do in your own application. I think we should probably update this to show examples both with and without a prefix, because not using one (and just putting the Relay endpoint on a different port from whatever other endpoints the application might have) may be a somewhat more common use case. But in the meantime this makes the current example less wrong.