A couple of changes to http://j-core.org/#download_bitstream made it easy for me to get going:

• In order to make ModemManager not try to think it’s a “modem”, create /etc/udev/rules.d/52-numato.rules with the following content:

  # Make ModemManager ignore Numato FPGA board
  ATTRS{idVendor}=="2a19", ATTRS{idProduct}=="1002", ENV{ID_MM_DEVICE_IGNORE}="1"

• You will need to install python3-pyserial and minicom
• The minicom command line i used was:

  sudo stty -F /dev/ttyACM0 -crtscts && minicom -b 115200 -D /dev/ttyACM0

and along with the instructions on j-core.org, I got it to load a known good build.