Add example repo to README

Hi!

Thanks for all the work put into this project. It's really great.

I would like offer up a link to an example repo I've created. I was thinking that maybe this could be included in the README under the "examples" section.

It took me a while to figure out a few critical details for my use-case, so I thought that it may help others to have a complete example. I believe my project is a decent example (granted it's new and probably could be refined) of the following cases:

• grpc-gateway handler within another (more standard) router, such as Chi
• custom base path for all grpc routing with the openapi configuration to support
• embedded Swagger UI without additional tooling

The demo project also details a few different patterns for defining and interacting with RPCs.