[beta] better docs for modelFor
[beta] better docs for modelFor

I wanted to stress that its main utility was for
accessing models on parent routes rather than
giving the impression that it's useful/meaningful
for grabbing models from any ol route, even if
it's not in the current route hierarchy, which
doesn't really make sense, right?

mmpestorich/ember.js,mmpestorich/ember.js,mmpestorich/ember.js