Improve documentation for parallel_tool_calls in ModelSettings

Author: Rehan-Ul-Haq

src/agents/model_settings.py

@@ -36,8 +36,13 @@ class ModelSettings:
     """The tool choice to use when calling the model."""
 
     parallel_tool_calls: bool | None = None
-    """Whether to use parallel tool calls when calling the model.
-    Defaults to True if not provided."""
+    """Controls whether the model can make multiple parallel tool calls in a single turn.
+    If not provided (i.e., set to None), this behavior defers to the underlying
+    model provider's default. For most current providers (e.g., OpenAI), this typically
+    means parallel tool calls are enabled (True).
+    Set to True to explicitly enable parallel tool calls, or False to restrict the
+    model to at most one tool call per turn.
+    """
 
     truncation: Literal["auto", "disabled"] | None = None
     """The truncation strategy to use when calling the model."""