There is a 5 pin jack on the controller box that has inputs for limit switches and emergency stop. This is because the same controller is used in our bigger 200mm Coil Winding Machine that we do a Emergency Stop and Limit/Homing kit for.
This kit will also work on the Mini but it is bulky and your other option is to install a simple micro switch that is normally open contacts and wire between GND and Left limit input . This can be wired into a Jack plug or the connector blocks on the controller pcb.
By default limit switches get turned off when the software detects the Mini but you can still go into Settings/Diagnostics and turn it on. But next time you run the software it will un-tick it again, so you would have to keep setting it. If you wanted to stop the software doing this then there is a jumper on the ARM Controller MKII that will set the controller as a custom machine. The software will then allow you to set up the machine as a Custom Machine and save the settings you put in.
You can set the Mini to be a custom machine and see how to wire the limit switch into the controller is shown on this page http://www.ukcnc.net/index.php/coil-winder-controller-board/
Also here is a quick run down on how you can wire in a low cost micro switch to act as a Homing switch. http://www.ukcnc.net/index.php/fitting-homing-switch-to-mini-coil-winder/