docs: document producer-consumer example using golang-queue with NSQ

- Update title to "Producer-Consumer Example"
- Add a detailed description of the example using `golang-queue` with NSQ
- Introduce prerequisites section with Go 1.22+ and NSQ installation
- Add instructions for running the producer, including directory navigation and running the producer
- Add instructions for running the consumer, including directory navigation and running the consumer
- Add an explanation section detailing the roles of the producer and consumer
- Ensure NSQ is running and accessible before starting the producer and consumer

Signed-off-by: appleboy <[email protected]>

_example/producer-consumer/README.md

@@ -1,29 +1,47 @@
-# Example with server and client
+# Producer-Consumer Example
 
-Please refer the following steps to build server and client.
+This example demonstrates how to use the `golang-queue` library with NSQ to implement a producer-consumer pattern.
 
-## Build server
+## Prerequisites
+
+- Go 1.22 or later
+- [NSQ](https://nsq.io/) installed and running
+
+## Running the Producer
+
+The producer sends tasks to the NSQ topic.
+
+Navigate to the producer directory:
 
 ```sh
-go build -o app server/main.go
+cd _example/producer-consumer/producer
 ```
 
-## Build client
+Run the producer:
 
 ```sh
-go build -o agent client/main.go
+go run main.go
 ```
 
-## Usage
+## Running the Consumer
 
-Run the multiple agent. (open two console in the same terminal)
+The consumer processes tasks from the NSQ topic.
+
+Navigate to the consumer directory:
 
 ```sh
-./agent
+cd _example/producer-consumer/consumer
 ```
 
-Publish the message.
+Run the consumer:
 
 ```sh
-./app
+go run main.go
 ```
+
+## Explanation
+
+- The producer creates a pool of workers and assigns tasks to the queue.
+- The consumer listens to the NSQ topic and processes the tasks.
+
+Ensure that NSQ is running and accessible at `127.0.0.1:4150` before starting the producer and consumer.