Fix #1494 by adding a link to Responses API documentation (#1502)

This pull request resolves #1494

Author: seratch

src/agents/model_settings.py

@@ -92,7 +92,10 @@ class ModelSettings:
     """
 
     truncation: Literal["auto", "disabled"] | None = None
-    """The truncation strategy to use when calling the model."""
+    """The truncation strategy to use when calling the model.
+    See [Responses API documentation](https://platform.openai.com/docs/api-reference/responses/create#responses_create-truncation)
+    for more details.
+    """
 
     max_tokens: int | None = None
     """The maximum number of output tokens to generate."""