Explain relations to CloudEvents (#19)

Explain relations to CloudEvents

Signed-off-by: Mattias Linnér <mattias.linner@ericsson.com>

primer.md

@@ -8,13 +8,34 @@ This non-normative document provides an overview of the CDEvents specification.
 
 <!-- toc -->
 - [History](#history)
+- [Relations to CloudEvents](#relations-to-cloudevents)
 - [Acknowledgments](#acknowledgments)
 <!-- /toc -->
 
 ## History
 
 TBD
 
+## Relations to CloudEvents
+
+CDEvents defines a [specification](./cloudevents-binding.md) that provides a set
+of JSON object schemas (one for each event type, covering mandatory and optional
+attributes etc.)
+
+When used with CloudEvents, CDEvents passes the JSON schema  via the
+[`dataschema`](https://github.com/cloudevents/spec/blob/v1.0.1/spec.md#dataschema)
+attribute and provide the corresponding JSON object through the
+[`data`](https://github.com/cloudevents/spec/blob/v1.0.1/spec.md#event-data)
+attribute.
+
+CDEvents aims to use existing CloudEvents extension attributes (e.g.
+`partitionkey` from the
+[Partitioning](https://github.com/cloudevents/spec/blob/v1.0.1/extensions/partitioning.md)
+extension) before defining its own extensions. When no appropriate extension
+attributes exists, CDEvents aims to make an official CloudEvents extension for
+the CloudEvents specification and listed with other [documented
+extensions](https://github.com/cloudevents/spec/blob/v1.0.1/documented-extensions.md).
+
 ## Acknowledgments
 
 The initial structure of the CDEvents specification format was based on the specification of the [CloudEvents](https://github.com/cloudevents/spec) project.