Draft: simple update description guidelines

[Kevin Kofler]

Richard Hughes wrote:
> This IS useful:
> https://admin.fedoraproject.org/updates/hwdata-0.222-1.fc10
> 
> This IS NOT useful:
> https://admin.fedoraproject.org/updates/gromacs-4.0.3-2.fc10

Those are indeed good examples.

        Kevin Kofler