[DOC release] Update ember-glimmer top-level documentation.

- Tweak wording to mention Glimmer supports a subset of Handlebars
- Update code samples to use documentation file paths

Author: locks

packages/ember-glimmer/lib/index.js

@@ -1,23 +1,19 @@
 /**
-  [Glimmer](https://github.com/tildeio/glimmer) is a [Handlebars](http://handlebarsjs.com/)
-  compatible templating engine used by Ember.js.
-  Any valid Handlebars syntax is valid in an Ember template.
+  [Glimmer](https://github.com/tildeio/glimmer) is a templating engine used by Ember.js that is compatible with a subset of the [Handlebars](http://handlebarsjs.com/) syntax.
 
   ### Showing a property
 
   Templates manage the flow of an application's UI, and display state (through
   the DOM) to a user. For example, given a component with the property "name",
   that component's template can use the name in several ways:
 
-  ```javascript
-    // app/components/person.js
+  ```app/components/person.js
     export default Ember.Component.extend({
       name: 'Jill'
     });
   ```
 
-  ```handlebars
-  {{! app/components/person.hbs }}
+  ```app/components/person.hbs
   {{name}}
   <div>{{name}}</div>
   <span data-name={{name}}></span>