Modern computers are no longer supplied with serial ports (other than Ethernet and USB), and even back when they did they were supplied, they were RS-232. Even then to get an RS-485 connection, you'll need a converter.
There are ton of high quality converters from companies like B&B Electronics (http://www.bb-elec.com/), but if all you want is an inexpensive 2-wire USB to RS-485 converter, this one (https://www.amazon.com/JBtek-Converter-Adapter-ch340T-Supported/dp/B00NKAJGZM/ref=sr_1_3) has been tested and works fine with the VBA_COMMS program (https://pps2.com/smf/index.php/topic,29.msg39.html#msg39).
Don't expect it to withstand the rigors of an industrial environment, but if you are looking for a low cost way of programming the Modbus MINT, this is a great choice (at least in February 2018 when this article was written).
(https://pps2.com/images/smf/mmint/low_cost_485_wide.jpg)
(https://pps2.com/images/smf/mmint/low_cost_485_closeup.jpg)
Here's a wiring diagram showing how the JBTech USB to RS485 adapter would be wired to the Modbus MINT (mMINT). Note that I used electrical tape to secure the cable to the USB adapter. The screw terminal landing on the USB adapter is not very robust.
(https://pps2.com/images/smf/mmint/JBTech_USB_485_to_mMINT.jpg)