Add troubleshooting information to the jumper section

[Boxxbeidl]

While following the build I didn't pay attention to the orientation of the board and set the jumpers on the wrong side of the PCB for one half. I noticed this too late when I had everything else soldered in place, controllers flashed and wanted to connect the two halves.

While it's not a big issue especially for newcomers this could be frustrating since the first thought would be "Now I have to desolder all the switches to fix this".

If you could add a sentence stating that in this case flipping the jumpers on the easily accessible side would be the easiest solution this would be very helpful.

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