Merge pull request #18 from j1m-ryan/describe-about-api

Add description of the About API

Author: k8s-ci-robot

site-src/concepts/about-api.md

@@ -1 +1,34 @@
-# About API Overview
+# About API Overview
+
+This document provides an overview of the About API.
+
+![Alt](../images/about-api.png "About API")
+
+The About API allows metadata to be attached to individual clusters. 
+The fundamental resource defined in the API is the ClusterProperty CRD.
+
+You can read more details about the API in [KEP-2149](https://github.com/kubernetes/enhancements/tree/master/keps/sig-multicluster/2149-clusterid).
+
+## ClusterProperty CRD
+
+The ClusterProperty CRD is proposed to give a Kubernetes-native way of identifying clusters, however, it can be used to store any metadata about a cluster. 
+
+### Example
+
+```
+apiVersion: about.k8s.io/v1
+kind: ClusterProperty
+metadata:
+  name: cluster.clusterset.k8s.io
+spec:
+  value: cluster-1
+```
+
+In the above example the ClusterProperty CRD is used to identify a cluster with the id of `cluster-1`. The key in this example `cluster.clusterset.k8s.io`, is one of the two proposed well-known properties. 
+
+### Well-known properties
+There are two well-known properties proposed:
+
+- `cluster.clusterset.k8s.io` A unique ID or name of the cluster. The value is implementation-specific, but it should be unique within the scope of the cluster set.  
+- `clusterset.k8s.io` The cluster set that the cluster belongs to. A cluster which is part of a cluster set should have this property set. 
+