First, make sure you understand how to use the USB properly so you don't damage your CR, if you plan to have it connected to an earth Grounded circuit. Many warnings on that in this forum and in the guide.
And you dont see serial output because it outputs to Serial by default (the BT header), not SerialUSB. If you want it to unconditionally output to SerialUSB you will have to change a few lines of code to SerialUSB instead:
You have to remove BT_found and change the Serial to SerialUSB in this loop() code:
if (BT_found && millis() - btInterval > BT_REFRESH_INTERVAL) //refresh rate (ms)
{
btInterval = millis();
readVOUT();
float VOUT = ((readDiff)/4096.0)*LDO_OUTPUT*1000*(OFFSET?1:OUTPUT_CALIB_FACTOR);
#if defined BT_OUTPUT_ADC
Serial.println(readDiff,0);
#elif defined BT_OUTPUT_AMPS
Serial.print(VOUT); Serial.print("E"); Serial.println(RANGE_NA ? -9 : RANGE_UA ? -6 : -3);
#elif defined BT_OUTPUT_NANOS
Serial.println(VOUT * (RANGE_NA ? 1 : RANGE_UA ? 1000 : 1000000));
#endif
}