Updated copy on section error to include student enrollment example.

@rocha @clintonb @lamagnifica 

![screen shot 2014-10-01 at 11 23 23 am](https://cloud.githubusercontent.com/assets/5265058/4477557/f7be1b30-497e-11e4-97c1-0bf878436820.png)

Ideally we would a way to set the value of the message dynamically, maybe using the database. That way we don't have to make a redeploy if there is a change in the data. This is a bit out of scope, and like we discussed, it should be fine if for now we extract the whole message and set it somewhere else, maybe in the configuration.