Update README.md

Added clearer instructions for starting the server before running the client.

Examples/hello-world-urlsession-client-example/README.md

@@ -14,7 +14,23 @@ The server can be started by running any of the Hello World server examples loca
 
 ## Usage
 
-Build and run the client CLI using:
+Start one of the Hello World servers in a different terminal:
+
+```console
+% cd Examples/hello-world-hummingbird-server-example
+% swift run
+2024-12-17T09:54:40-0600 info HummingBird : [HummingbirdCore] Server started and listening on 127.0.0.1:8080
+```
+
+or
+
+```console
+% cd Examples/hello-world-vapor-server-example
+% swift run
+2024-12-17T10:34:55-0600 notice codes.vapor.application : [Vapor] Server started on http://127.0.0.1:8080
+```
+
+Then, build and run the client CLI using:
 
 ```console
 % swift run