Instead of sharing the cloud settings, I just uploaded an atmosphere file, it's easier. This is just the default atmosphere with these clouds added. Feel free to use it or change it (it would be nice if you could give me credit if you use it, but not mandatory, it's up to you).

Word of warning: these clouds are slow to render and they tend to be grainy (specially if used with volumetric sunlight). You should raise AA settings to at least 95% and max subrays minimum 16.
These clouds generate godrays very easily. Just put the sun in front of them and enable godrays and very likely you'll see godrays. These were the clouds to generate godrays in "shepherd of dragons" or in "road to tertius: between the sun and the moon".

http://download.yousendit.com/7ECDFBB41190D369

This file will be online for just 7 days and then it will be automatically deleted by the host.