Clarify that IS-13 acts on the same resources as IS-04

[peterbrightwell]

I received a question along the lines of "Are the labels, descriptions and tags in IS-13 the same resources as in IS-04 Node API?". I've answered yes (as it's the point of IS-13), and that the draft test suite reads with IS-04 and compares what was written in IS-13 but perhaps this could be stated more directly somewhere in the text?