mention ClusterPool as method for SelfProvisioning

[ch-stark]

Within ACM today, the best way for developers to obtain the cluster would be using the ClusterPools feature. since the cluster is well defined in the ClusterPool itself, the developer claims a new cluster from the pool by giving it a name and the cluster itself comes out of hibernation, ready for use. Meanwhile a new cluster then gets built and added into the ClusterPool, hibernated and waiting for the next user