Link to the protobuf generated code guide

Signed-off-by: Nic Cope <[email protected]>

Author: negz

README.md

@@ -10,6 +10,13 @@ guidelines] as Crossplane.
 To learn how to use this SDK:
 
 * [Learn about how composition functions work][functions]
+* [Learn about Python code generated from protocol buffers][python-protobuf]
+
+The `RunFunctionRequest` and `RunFunctionResponse` types provided by this SDK
+are generated from a proto3 protocol buffer schema. Their fields behave
+similarly to built-in Python types like lists and dictionaries, but there are
+some differences. Read the generated code documentation to familiarize yourself
+with the the differences.
 
 ## Contributing
 
@@ -35,5 +42,6 @@ hatch build
 
 [python]: https://python.org
 [functions]: https://docs.crossplane.io/latest/concepts/composition-functions
+[python-protobuf]: https://protobuf.dev/reference/python/python-generated/
 [contributing guidelines]: https://github.com/crossplane/crossplane/tree/master/contributing
 [hatch]: https://github.com/pypa/hatch