Add documentation for the Outlines model

Author: RobinPicard

docs/models/outlines.md

@@ -136,6 +136,7 @@ from pydantic_ai.models.outlines import OutlinesModel
 from pydantic_ai.settings import ModelSettings
 
 class Box(BaseModel):
+    """Class representing a box"""
     width: int
     height: int
     depth: int