You can kind of see the round side is facing up, the growth of the root and the top side plant both come out of the "pointy" end.
If for some reason the root is out and it turned towards the round side I would put the round side down versus having the root try to reverse direction.
Most of the nuts I got from bigeight, the root was either just starting to come straight out or turned towards the flat side.
Like others have said, the radical must be facing down weather the nut is on its flat side or not. Simply make a hole with your finger and place the radical in it and press dirt around it. Then just cover the nut lighty with soil.