More daemon option information

@jpetazzo @unclejack @alexlarsson @crosbymichael 

Can you please give us some other juicy tradeoffs between the storage drivers? 

I'm presuming that the statement I made about the lxc driver isn't too wrong, but that too needs review.

@jamtur01 @fredlf @ostezer - at this point, we have zero documentation helping users/admins decide which to use when - I _hope_ this is an improvement.
@alexlarsson / @paultag I get the feeling that if you have a systemd based system, the dameon is started with only `fd://`, but the docker client doesn't know about it - so it fails, complaining that it can't find a docker daemon on the unix socket (I had this happen when debian upgraded my box to systemd - is there some cleverness that should be implemented on that end?