Here is the basic circuit.
The Pi PCB board ( both the Zero and the larger rasp Pi 2 and 3 versions) feature a connection point where you can add a 2 pin header and create a remote reboot switch. on the rasp pi 2 and three you can see it here:
im building a little board with 8 transistor switches so i can reboot up to 8 Pi's remotely, from a master controller ( here a Raspi Zero)
ill post pics of the board and circuit shortly, and the results of the project.
update 1: i the reset button seems to work with the Zero, but for some reason the LED isnt lighting. still working on it...
Next im going to set up a rasp pi 2b with a header on the run/ground connection and then test the reset with that.
it looks like the prototype will have 5 channels. hopefully 4 of them will work....