chore(example): Autoreloading server example (#316)

* Create an example of an autoreloading server

* Document the autoreloading server example

* Format autoreloading server example

* Add note about cargo-watch in the examples readme

examples/src/autoreload/server.rs

@@ -0,0 +1,49 @@
+use tonic::{transport::Server, Request, Response, Status};
+
+use hello_world::greeter_server::{Greeter, GreeterServer};
+use hello_world::{HelloReply, HelloRequest};
+
+pub mod hello_world {
+    tonic::include_proto!("helloworld");
+}
+
+#[derive(Default)]
+pub struct MyGreeter {}
+
+#[tonic::async_trait]
+impl Greeter for MyGreeter {
+    async fn say_hello(
+        &self,
+        request: Request<HelloRequest>,
+    ) -> Result<Response<HelloReply>, Status> {
+        println!("Got a request from {:?}", request.remote_addr());
+
+        let reply = hello_world::HelloReply {
+            message: format!("Hello {}!", request.into_inner().name),
+        };
+        Ok(Response::new(reply))
+    }
+}
+
+#[tokio::main]
+async fn main() -> Result<(), Box<dyn std::error::Error>> {
+    let addr = "[::1]:50051".parse().unwrap();
+    let greeter = MyGreeter::default();
+
+    println!("GreeterServer listening on {}", addr);
+
+    let server = Server::builder().add_service(GreeterServer::new(greeter));
+
+    match listenfd::ListenFd::from_env().take_tcp_listener(0)? {
+        Some(listener) => {
+            let mut listener = tokio::net::TcpListener::from_std(listener)?;
+
+            server.serve_with_incoming(listener.incoming()).await?;
+        }
+        None => {
+            server.serve(addr).await?;
+        }
+    }
+
+    Ok(())
+}