Update References.md.hbs

[dagnelies]

To clarify #2432

[fskreuz]

It's kinda mentioned in the paragraph before it 😉

Note that this is the root of the ractive instance in which the template appears, not the entire view hierarchy of nested components.

[dagnelies]

hmmm... yeah ...right. Nevertheless that sentence isn't very straightforward.
Let me close the other pull request, here is a clarified statement: #250

[dagnelies]

To clarify it: ("this is the root of the ractive instance in which the template appears") actually sounds like the ractive instance is the root, which is not the case.