Add purchasing additional resource (#467)

Author: bhardesty

docs/kafka/getting-started-kafka/README.adoc

@@ -307,6 +307,7 @@ endif::[]
 
 [role="_additional-resources"]
 == Additional resources
+* https://console.redhat.com/application-services/streams/overview[Purchase a subscription to {product-long-kafka}]
 * https://access.redhat.com/documentation/en-us/red_hat_openshift_streams_for_apache_kafka/1/guide/7d28aec8-e146-44db-a4a5-fafc1f426ca5[_Configuring topics in {product-long-kafka}_^]
 * {base-url}{rhoas-cli-getting-started-url-kafka}[_Getting started with the `rhoas` CLI for {product-long-kafka}_^]
 * {rhoas-cli-base-url}{rhoas-cli-ref-url}[_CLI command reference (rhoas)_^]