Encourage good naming of syntax themes

There were a number of syntax themes popping up on twitter that were just named something like 'cool-theme'. This pull encourages them to suffix with `-syntax`. Minor, but I would really like to have a naming convention for themes. 

![screen shot 2014-02-27 at 4 13 53 pm](https://f.cloud.github.com/assets/69169/2289775/b82fb35e-a00d-11e3-896d-e27dec9a8b95.png)