added info

README.md

   * Sitemap generation
   * Incremental builds
   * Analytics via Google
-  * Comments via [Disqus](http://disqus.com/)
+  * Comments via [Disqus](http://disqus.com/) or [isso](http://posativ.org/isso)
   * Hosting via [Github Pages](https://pages.github.com/) or [Amazon S3](http://aws.amazon.com/s3/)
   * Embedding [gfycats](http://gfycat.com/)
   * [Tweeting](http://twitter.com/) about new posts