UART is on the 8 pins next to the buttons - exactly what the image shows. I have it working fine even though the guide is not very helpful - there are no clear instructions on how to wire it (the very few may even be wrong - VCC and TX2 are not required at all, I just needed GND, TX3 and RX3).
What I want to know are the 4 pins on the opposite side of the board, next to the ethernet port - 3 of them are labeled 5V, D+, D- and if we assume the last one with no label is GND, this forms a USB port that I am asking about.