Warning: Backup your important data before using USB as it will overwrite anything on the USB key.
Download a netboot.xyz USB disk:
Insert a USB key in your compute and find the device name. Then use following command:
cat ipxe.usb > /dev/sdX
or
dd if=ipxe.usb of=/dev/sdX
where sdX is your usb drive.
The USB key should be ready to eject once finished.
Run:
diskutil list
to get the current list of devices
Insert the flash media.
Run:
diskutil list
again and determine the device node assigned to your flash media (e.g. /dev/disk2).
Run:
diskutil unmountDisk /dev/diskN
(replace N with the disk number from the last command; in the previous example, N would be 2).
Execute:
sudo dd if=netboot.xyz.usb of=/dev/rdiskN bs=1m
Run:
diskutil eject /dev/diskN
and remove your flash media when the command completes.
Check out Rufus to install the ISO file to a USB key.
Once you've created your key, reboot and set your BIOS to load the USB key first if it's not set for that already. You should see iPXE load up either load up netboot.xyz automatically or prompt you to set your networking information up.