The board definition of the `nrf52dk` was likely created for some clone
board. However, an official board name nRF52 DK provided by Nordic
also exists. This resulted in previous contributors in confusing this
with the official board and "fixing" the board definition to match
the nRF52 DK board.
Or maybe it always has been meant to be the official board and someone
just added a wrong image to it.
In either case, this brings the documentation back in alignment with
the code by replacing references to some random clone board and the
image of the random clone board with those to/of the official Nordic
nRF52 DK board.
