Update "dynamic segments" section

Update "dynamic segments" section according to Ember Data transition document, more details at https://github.com/emberjs/data/blob/master/TRANSITION.md

Note: source comments should change accordingly, see https://github.com/emberjs/ember.js/blob/master/packages/ember-routing/lib/system/route.js
Merge pull request #771 from potomak/patch-1

Update "dynamic segments" section