The ArduinoUSBLinker is a project of LittleMo, for more information see the readme on github.
To create a ArduinoUSBLinker you need an Arduino with on-board FTDI preferred. Before you can do anything plug it to your PC or Mac and check if it is recognized by the operating system. If not you may get a message to install a driver for the FTDI chip. When the driver is installed, go to the device manager and note down what port or device is associated to the Arduino when it is plugged to your computer.
You need a internet connection to load the firmware during the flashing.
Don't forget to choose the ArduinoUSBLinker and enable the default baud rate again, before you update your bootloader enabled SimonK ESC.