Document the missing `DisableNetwork` config flag to /containers/create end-point

There seems to be [need to have CLI's `-n=false` in the remote api](https://twitter.com/NetRoY/status/445289970836996097) as well. 
It exists, but isn't documented..
Couldn't find any documentation on the other flags, so I'm guessing updating the sample payload is good enough for now.