Improve documentation for RouterService and mount helper

Fixes #15622

Author: locks

packages/ember-glimmer/lib/syntax/mount.js

@@ -27,10 +27,32 @@ function dynamicEngineFor(vm, args, meta) {
   {{mount "ember-chat"}}
   ```
 
-  Currently, the engine name is the only argument that can be passed to
-  `{{mount}}`.
+  Additionally, you can also pass in a `model` argument that will be
+  set as the engines model. This can be an existing object:
+  
+  ```
+  <div>
+    {{mount 'admin' model=userSettings}}
+  </div>
+  ```
+
+  Or an inline `hash`, and you can even pass components:
+
+
+  ```
+  <div>
+    <h1>Application template!</h1>
+    {{mount 'admin' model=(hash
+        title='Secret Admin'
+        signInButton=(component 'sign-in-button')
+    )}}
+  </div>
+  ```
 
   @method mount
+  @param {String} name Name of the engine to mount.
+  @param {Object} [model] Object that will be set as
+                          the model of the engine.
   @for Ember.Templates.helpers
   @category ember-application-engines
   @public

packages/ember-routing/lib/services/router.js

@@ -18,9 +18,41 @@ import { shallowEqual } from '../utils';
    @category ember-routing-router-service
  */
 const RouterService = Service.extend({
+
+  /**
+     Name of the current route.
+
+     @property currentRouteName
+     @type String
+     @public
+   */
   currentRouteName: readOnly('_router.currentRouteName'),
+
+  /**
+     Current URL for the application.
+
+     @property currentURL
+     @type String
+     @public
+   */
   currentURL: readOnly('_router.currentURL'),
+
+  /**
+     Location object for the application.
+
+     @property location
+     @type String
+     @public
+   */
   location: readOnly('_router.location'),
+
+  /**
+     Root URL of the current application.
+
+     @property rootURL
+     @type String
+     @public
+   */
   rootURL: readOnly('_router.rootURL'),
   _router: null,