Add posts.show route

`ember g route posts/show`

Outer red:
✘ Element .js-post-detail-title exists
✘ Element .js-post-detail-body exists

Now the acceptance test is able to display the `posts.show` route, but it can't find the post's title on the page, because we aren't rendering anything to the screen yet.

app/router.js

@@ -9,6 +9,7 @@ const Router = EmberRouter.extend({
 Router.map(function() {
   this.route('posts', function() {
     this.route('new');
+    this.route('show');
   });
 });
 

app/routes/posts/show.js

@@ -0,0 +1,4 @@
+import Route from '@ember/routing/route';
+
+export default Route.extend({
+});

app/templates/posts/show.hbs

@@ -0,0 +1 @@
+{{outlet}}

tests/unit/routes/posts/show-test.js

@@ -0,0 +1,11 @@
+import { moduleFor, test } from 'ember-qunit';
+
+moduleFor('route:posts/show', 'Unit | Route | posts/show', {
+  // Specify the other units that are required for this test.
+  // needs: ['controller:foo']
+});
+
+test('it exists', function(assert) {
+  let route = this.subject();
+  assert.ok(route);
+});