REST Docs: memory quota should be for a node, not a cluster

The current text reads:
Before a node can be used in a cluster, a few things may need to be configured. Specifically, if creating a new cluster, the memory quota per node for that cluster must be set. Whether the node is joining an existing cluster or starting a new cluster, it's storage path must be configured.

and then:
Configuring a cluster's memory quota.

Memory quota is per-node, so it shouldn't be referred to as a cluster memory quota.