docs: section about custom source and sink types

developer/wip/for-contributors/contributor-handbook.md

@@ -200,6 +200,12 @@ information about it and other topics such as data plane self-registration and p
 
 ### 4.2 Writing a custom data plane extension (sink/source)
 
+The EDC Data Plane is build on top of the *Data Plane Framework (DPF)*, which can be used for building custom data planes.
+ The framework has extensibility points for supporting different data sources and sinks (e.g., S3, HTTP, Kafka) and can perform direct streaming between different source and sink types.
+
+Detailed documentation about writing a custom data plane extension can be found [here](./data-plane/data-plane-extensions.md)
+
+
 ### 4.3 Writing a custom data plane (using only DPS)
 
 ## 5. Development best practices