docs(pass_through.md): add doc on using langfuse client sdk w/ litellm proxy

docs/my-website/docs/proxy/pass_through.md

@@ -193,6 +193,53 @@ curl --request POST \
   }'
 ```
 
+### Use Langfuse client sdk w/ LiteLLM Key 
+
+**Usage** 
+
+1. Set-up yaml to pass-through langfuse /api/public/ingestion
+
+```yaml
+general_settings:
+  master_key: sk-1234
+  pass_through_endpoints:
+    - path: "/api/public/ingestion"                                # route you want to add to LiteLLM Proxy Server
+      target: "https://us.cloud.langfuse.com/api/public/ingestion" # URL this route should forward 
+      auth: true # 👈 KEY CHANGE
+      custom_auth_parser: "langfuse" # 👈 KEY CHANGE
+      headers:
+        LANGFUSE_PUBLIC_KEY: "os.environ/LANGFUSE_DEV_PUBLIC_KEY" # your langfuse account public key
+        LANGFUSE_SECRET_KEY: "os.environ/LANGFUSE_DEV_SK_KEY"     # your langfuse account secret key
+```
+
+2. Start proxy
+
+```bash
+litellm --config /path/to/config.yaml
+```
+
+3. Test with langfuse sdk
+
+
+```python
+
+from langfuse import Langfuse
+
+langfuse = Langfuse(
+    host="http://localhost:4000", # your litellm proxy endpoint
+    public_key="sk-1234",        # your litellm proxy api key 
+    secret_key="anything",        # no key required since this is a pass through
+)
+
+print("sending langfuse trace request")
+trace = langfuse.trace(name="test-trace-litellm-proxy-passthrough")
+print("flushing langfuse request")
+langfuse.flush()
+
+print("flushed langfuse request")
+```
+
+
 ## `pass_through_endpoints` Spec on config.yaml
 
 All possible values for `pass_through_endpoints` and what they mean