UART is broken out to the unpopulated switch header at the front of the
board.
This isn't quite the same as the V2.0 definition as the system led is
always on, not routed through the CPU.
Additionally, document that the newer revision of the same "YS25-0402"
is supported via the existing PCB-K0402WS-V3.0 target.
I recently brought a "Ztyuav Z-QWYT0402", the insides looked identical to the
existing supported "Hisource Hi-K0402WS". Both of them have the
"PCB-K0402-V3.0" silkscreen.
I flashed the vanilla image and it seems to work great.
I changed the documentation to be more inclusive of other devices (including
adding a picture of mine). I suspect more devices might fall into this
"PCB-K0402-V3.0" bucket, for example the "YuanLey YS25-0402" with
the vlan switch also looks suspiciously identical from the outside.
I also added some details I noticed while flashing mine:
teardown, flash padding, how the selector switch actually works.