Add page-title usage

Author: NullVoxPopuli

files/demo-app/templates/application.gts

@@ -1,6 +1,10 @@
+import { pageTitle } from 'ember-page-title';
+
 const greeting = 'hello';
 
 <template>
+  {{pageTitle "Demo App"}}
+
   <h1>Welcome to ember!</h1>
 
   {{greeting}}, world!