Swapped out placeholder text on teams admin page

Changed "simple Teams description" placeholder subtitle to "allow you
to organize groups of people that have a common focus. Use teams to
simplify the process of assigning roles to groups of people."

Before: 
![image](https://f.cloud.github.com/assets/2149341/451435/e95973de-b2ab-11e2-9897-0f2bbe6d44d7.png)

After: 
![image](https://f.cloud.github.com/assets/2149341/451436/ed37e968-b2ab-11e2-87b4-a34477c55a6f.png)