add readme file for kafka exporter addon

Author: spdeepak

addons/confluent-kafka/README.md

@@ -0,0 +1,107 @@
+# FlowTracker Kafka Exporter
+
+This is an addon for the [FlowTracker](https://github.com/spdeepak/flowtracker) library. It implements the `Exporter` interface to asynchronously push trace data to a **Apache Kafka** topic using the [confluent-kafka-go](https://github.com/confluentinc/confluent-kafka-go) library.
+
+## 📦 Installation
+
+Since this is an addon module, you must install it alongside the core library:
+
+```bash
+# Install Core
+go get github.com/spdeepak/flowtracker
+
+# Install Kafka Exporter
+go get github.com/spdeepak/flowtracker/kafka-exporter
+```
+
+*Note: This library uses `confluent-kafka-go` which requires CGO to be enabled.*
+
+## 🚀 Usage
+
+You can configure the exporter in two ways: letting the library manage the connection, or bringing your own producer.
+
+### Option 1: Simple Configuration (Library creates Producer)
+Use this if you want FlowTracker to manage the Kafka connection lifecycle.
+
+```go
+package main
+
+import (
+	"github.com/confluentinc/confluent-kafka-go/kafka"
+	"github.com/spdeepak/flowtracker"
+	"github.com/spdeepak/flowtracker/kafka-exporter"
+)
+
+func main() {
+	// 1. Configure the Exporter
+	exporter, err := kafkaexporter.New(kafkaexporter.Config{
+		Topic: "microservice-traces",
+		KafkaConfigMap: &kafka.ConfigMap{
+			"bootstrap.servers": "localhost:9092",
+			"client.id":         "flowtracker-exporter",
+			"acks":              "all",
+		},
+	})
+	if err != nil {
+		panic(err)
+	}
+	// Ensure outstanding messages are flushed on shutdown
+	defer exporter.Close()
+
+	// 2. Apply Middleware
+	mw := flowtracker.NewMiddleware(flowtracker.WithExporter(exporter))
+	
+	// ... start your server
+}
+```
+
+### Option 2: Reuse Existing Producer
+Use this if your application already has a Kafka Producer instance and you want to reuse the connection.
+
+```go
+func main() {
+    // Assuming 'myAppProducer' is your existing *kafka.Producer
+    
+    exporter, _ := kafkaexporter.New(kafkaexporter.Config{
+        Topic:    "microservice-traces",
+        Producer: myAppProducer,
+    })
+
+    mw := flowtracker.NewMiddleware(flowtracker.WithExporter(exporter))
+}
+```
+
+## 📝 Data Format
+
+The exporter sends data to Kafka in the following format:
+
+*   **Key:** The `trace_id` (String). This ensures all spans for a specific trace land on the same Kafka partition.
+*   **Value:** JSON String of the `Trace` object.
+
+**Example Payload:**
+```json
+{
+  "trace_id": "trace-1700234-99",
+  "spans": [
+    {
+      "span_id": "101",
+      "name": "GET /api/checkout",
+      "duration_ms": 150
+    },
+    {
+      "span_id": "202", 
+      "parent_id": "101",
+      "name": "DB: Process Order",
+      "duration_ms": 45
+    }
+  ]
+}
+```
+
+## 🔗 Examples
+
+You can find a complete, runnable example of how to use this exporter in the main repository:
+
+👉 **[Click here for the Kafka Example Code](../../examples/kafka)**
+
+*(Note: If the link above doesn't work, navigate to the `examples/kafka` directory in the repository root).*