Add new line after create action on CommentsController code example

Following PostsController basic authentication code example.

![getting started guide - 9 1 basic authentication screen shot 2013-09-27 at 4 57 21 pm](https://f.cloud.github.com/assets/360276/1224202/485c7d80-2742-11e3-891e-22921e2c7aea.png)