Add a bit more explanation about supporting organisations

Fixes #992.

Before:

![selection_002](https://cloud.githubusercontent.com/assets/48945/5257857/2402e9f0-7a35-11e4-88ba-3b706b665d9a.png)

After:

![selection_001](https://cloud.githubusercontent.com/assets/48945/5257859/2931a394-7a35-11e4-82e7-12d329c97fb1.png)

Thoughts @equivalentideas @mlandauer?