Document direct header usage in client constructors

Co-authored-by: Shri Sukhani <shrisukhani@users.noreply.github.com>

Author: cursoragent

README.md

@@ -24,7 +24,8 @@ export HYPERBROWSER_API_KEY="your_api_key"
 export HYPERBROWSER_BASE_URL="https://api.hyperbrowser.ai" # optional
 ```
 
-You can also pass custom headers (for tracing/correlation) via `ClientConfig`:
+You can also pass custom headers (for tracing/correlation) either via
+`ClientConfig` or directly to the client constructor.
 
 ```python
 from hyperbrowser import ClientConfig, Hyperbrowser
@@ -38,6 +39,18 @@ with Hyperbrowser(config=config) as client:
     ...
 ```
 
+```python
+from hyperbrowser import Hyperbrowser
+
+with Hyperbrowser(
+    api_key="your_api_key",
+    headers={"X-Correlation-Id": "req-123"},
+) as client:
+    ...
+```
+
+> If you pass `config=...`, do not also pass `api_key`, `base_url`, or `headers`.
+
 ## Clients
 
 The SDK provides both sync and async clients with mirrored APIs: