update langfuse docs

docs/my-website/docs/observability/langfuse_integration.md

@@ -144,6 +144,26 @@ print(response)
 
 ```
 
+You can also pass `metadata` as part of the request header with a `langfuse_*` prefix:
+
+```shell
+curl --location 'http://0.0.0.0:4000/chat/completions' \
+    --header 'Content-Type: application/json' \    
+    --header 'langfuse_trace_id: trace-id22' \
+    --header 'langfuse_trace_user_id: user-id2' \
+    --header 'langfuse_trace_metadata: {"key":"value"}'
+    --data '{
+    "model": "gpt-3.5-turbo",
+    "messages": [
+        {
+        "role": "user",
+        "content": "what llm are you"
+        }
+    ]
+}'
+```
+
+
 ### Trace & Generation Parameters
 
 #### Trace Specific Parameters