Add Disqus for community comments on posts

See:
* https://disqus.com

app/assets/javascripts/disqus.js

@@ -0,0 +1,21 @@
+/**
+ *  RECOMMENDED CONFIGURATION VARIABLES:
+ *  EDIT AND UNCOMMENT THE SECTION BELOW
+ *  TO INSERT DYNAMIC VALUES FROM YOUR PLATFORM OR CMS.
+ *  LEARN WHY DEFINING THESE VARIABLES IS IMPORTANT:
+ *  https://disqus.com/admin/universalcode/#configuration-variables
+*/
+
+/*
+var disqus_config = function () {
+    this.page.url = PAGE_URL;  // Replace PAGE_URL with your page's canonical URL variable
+    this.page.identifier = PAGE_IDENTIFIER; // Replace PAGE_IDENTIFIER with your page's unique identifier variable
+};
+*/
+
+(function() { // DON'T EDIT BELOW THIS LINE
+    var d = document, s = d.createElement('script');
+    s.src = '//the-self-destructing-blog.disqus.com/embed.js';
+    s.setAttribute('data-timestamp', +new Date());
+    (d.head || d.body).appendChild(s);
+})();

app/views/posts/show.html.erb

@@ -14,3 +14,7 @@
 </div>
 
 <%= link_to "Back", posts_path %>
+
+<div id="disqus_thread">
+  <noscript>Please enable JavaScript to view the comments.</noscript>
+</div>