add a screenshot

Author: paigecalvert

docs/vendor/testing-about.md

@@ -8,6 +8,10 @@ This topic describes Replicated Compatibility Matrix, including use cases, billi
 
 <Overview/>
 
+![Create cluster page in the vendor portal](/images/compatibility-matrix-create-cluster.png)
+
+[View a larger version of this image](/images/compatibility-matrix-create-cluster.png)
+
 You can use Compatibility Matrix with the Replicated CLI or the Replicated Vendor Portal. For more information about how to use Compatibility Matrix, see [Use Compatibility Matrix](testing-how-to).
 
 ## Supported Clusters and VMs