Doc request: Document administrative task of re-sizing with additional resources in Couchbase

As a specific section, document the best practices around changing the RAM size of the whole cluster via rebalance, quota change, etc.

Should be accompanied by description of when this might be used, the considerations invovled. Here is a writeup from support than should be used/adapted: http://support.couchbase.com/entries/21719273-How-to-Reduce-the-RAM-size-on-an-existing-Couchbase-cluster-without-shutting-down-the-cluster