docs: Mention bi-directional streaming

Author: pojntfx

README.md

@@ -6,7 +6,7 @@ Backend for an example chat application using the `go-app` package and gRPC over
 
 ## Overview
 
-`go-app-grpc-chat-backend` is a short example showing the use of the [go-app](https://github.com/maxence-charriere/go-app) package and [gRPC](https://grpc.io/). This is the backend, which echoes messages back to the frontend and add's the server's timestamp to them.
+`go-app-grpc-chat-backend` is a short example showing the use of the [go-app](https://github.com/maxence-charriere/go-app) package and [gRPC](https://grpc.io/). This server uses gRPC bi-directional streaming to publish/subscribe chat messages to all clients.
 
 ## Installation