fix: update hello_world example to remove etcd (#5422)

Signed-off-by: Neal Vaidya <nealv@nvidia.com>

examples/custom_backend/hello_world/README.md

@@ -48,36 +48,27 @@ The example demonstrates:
 
 ## Getting Started
 
-## Prerequisites
+### Prerequisites
 
- Before running this example, ensure you have the following services running:
-
- - **etcd**: A distributed key-value store used for service discovery and metadata storage
- - **NATS**: A high-performance message broker for inter-component communication
-
- You can start these services using Docker Compose:
-
- ```bash
- # clone the dynamo repository if necessary
- # git clone https://github.com/ai-dynamo/dynamo.git
- cd dynamo
- docker compose -f deploy/docker-compose.yml up -d
- ```
+Dynamo must be installed. No external services are required for local development—the example uses file-based KV storage by default.
 
 ### Running the Example
 
 First, start the backend service:
 ```bash
 cd examples/custom_backend/hello_world
-python hello_world.py
+DYN_STORE_KV=file python hello_world.py
 ```
 
 Second, in a separate terminal, run the client:
 ```bash
 cd examples/custom_backend/hello_world
-python client.py
+DYN_STORE_KV=file python client.py
 ```
 
+> **Note**: Setting `DYN_STORE_KV=file` uses file-based storage instead of etcd.
+> Both the backend and client must use the same KV backend to discover each other.
+
 The client will connect to the backend service and print the streaming results.
 
 ### Expected Output