Adding in note re logged in user missing during post creation

missing true example code until someone recreates locally and copy+pastas or screenshots.
Notes that later homework example fixes the problem correctly.

fixes #68
![anonymous_post_new_error](https://cloud.githubusercontent.com/assets/3831860/3713396/b854141e-1566-11e4-906c-11be24af993f.png)

Is the error you get when anonymously creating blog posts...