EmberJS 2.7 - how to bind attribute 'disabled' for a button

This official guide describes how you can bind a boolean property to disabled attribute of a HTML element. Yet it talks about a controller.

I have a button, that when clicked transitions the route (sorry it has to be a button and cannot be a link-to):

/templates/trails.hbs

<button type="button" class="btn btn-primary" disabled= 
              onclick=>Add New</button>

(route-action is a helper that allows me to use closure actions in routes)

/routes/trails.js

import Ember from 'ember';

export default Ember.Route.extend({
  actions: {
    addNew() {
      this.transitionTo('trails.new');
    } 
  }
});

So, after the button is clicked, the route is changed to 'trails.new'

/routes/trails/new.js

import Ember from 'ember';

export default Ember.Route.extend({
  isEditing: true,
});

This property appears to be ignored and is not bound as I had expected it would be. I also tried adding a controller:

/controllers/trails/new.js

import Ember from 'ember';

export default Ember.Controller.extend({
  isEditing: true,
});

So how does the official guide suggest something that seems to not work? What piece of ember magic am I missing here?