Add description to name field in author fieldset on node form.

#6002 

Output for Publication form:
![selection_123](https://cloud.githubusercontent.com/assets/4497748/2838580/c5355352-d036-11e3-8360-2564056ea734.png)

And for other node types:
![selection_128](https://cloud.githubusercontent.com/assets/4497748/2850016/2f284576-d0f0-11e3-9672-347fc3855bd1.png)