Point to ember-data-storefront instead of ember-cached-shoe

See Appchance/ember-cached-shoe#11

As I stated there, ember-cached-shoe doesn't seem to be actively maintained anymore, and ember-data-storefront provides the same functionality out of the box.

So this PR changes the "Think out of the Shoebox" section to suggest ember-data-storefront instead of ember-cached-shoe.

Author: Dan Wenzel

README.md

@@ -380,24 +380,24 @@ export default Ember.Route.extend({
 
 Shoebox gives you great capabilities, but using it in the real app is pretty rough. Have you ever thought that such kind of logic should be done behind the scenes? In a large codebase, defining `fastboot.isFastboot` conditionals can be a daunting task. Furthermore, it generates a lot of boilerplate code, which obscures the solution. Sooner or later coupling with `shoebox` will spread over all routes.
 
-That's why [ember-cached-shoe](https://www.npmjs.com/ember-cached-shoe) was born.
+Fortunately, there is an addon called [ember-data-storefront](https://embermap.github.io/ember-data-storefront/) that can help to alleviate this pain, thanks to its Fastboot mixin: https://embermap.github.io/ember-data-storefront/docs/guides/fastboot.
 
-After installing and applying it, your routes can look like this:
+After installing the addon and applying the mixin, your routes can look like this:
 
 `app/routes/my-route.js`:
 
 ```javascript
-import Ember from 'ember'
+import Route from '@ember/routing/route';
 
-export default  Ember.Route.extend({
+export default  Route.extend({
   model() {
     // first call in a server makes actual ajax request.
     // second call in a browser serves cached response
     return this.store.findAll('posts')
   }
 })
 ```
-And they still take advantage of caching in the `shoebox`. No more redundant AJAX for already acquired data. Installation details are available in the addon [README](https://github.com/appchance/ember-cached-shoe#ember-cached-shoe).
+And they still take advantage of caching in the `shoebox`. No more redundant AJAX for already acquired data. Installation details are available in the addon [documentation](https://embermap.github.io/ember-data-storefront/docs).
 
 ### Rehydration