Add documentation note for Arrow C Data Interface PyCapsule in DataFrame class

Author: kosiew

python/datafusion/dataframe.py

@@ -1135,6 +1135,11 @@ def __arrow_c_stream__(self, requested_schema: object | None = None) -> object:
             >>> stream = df.__arrow_c_stream__(schema)
             >>> capsule = schema._export_to_c_capsule()
             >>> stream = df.__arrow_c_stream__(capsule)
+        
+        Notes:
+            The Arrow C Data Interface PyCapsule details are documented by Apache
+            Arrow and can be found at:
+            https://arrow.apache.org/docs/format/CDataInterface/PyCapsuleInterface.html
         """
         # ``DataFrame.__arrow_c_stream__`` in the Rust extension leverages
         # ``execute_stream_partitioned`` under the hood to stream batches while