Determine a rule-of-thumb for what content should be moved from the Ember Guides

@mehulkar and @Gaurav0 are working on this! This issue just helps to track that they are interested in helping, and also serve as a place where others can add comments.

The question we are trying to answer is, how do we know what content should be moved from ember.js guides to ember-cli guides? More broadly, is there a definition or description that will help us understand whether new content belongs in a certain guide?