Revise readme

[hmil]

Current readme may be a little confusing and doesn't even show how to bind the express router.

[erikhofer]

It would be helpful to write something about error handling in the router.

https://github.com/hmil/rest.ts/blob/27cc374bb564270cea8557e0329c401492467829/packages/rest-ts-express/src/index.ts#L99-L108

It's nice that you can simply throw exceptions in async handlers and they are forwarded to express error handlers. It is, however, not immediately obvious because this is not the case with vanilla express.