Do you want to have the fog lights come on when the parkers come on, or have them switchable but only when parkers are on? I would prefer the latter, here's how to do both plus an extra option of bringing on the fog lights independently.
You have a parker bulb in the headlight assembly, you'll need to work out which one is positive. Join a wire to this and connect it to pin 85 of the headlight relay. If you want the fog lights to come on ANY time with a switch you need to connect pin 85 to pin 30 and follow the rest of option 2 below.
All scenarios require a fuse connected directly to the battery and then connected to pin 30 of the relay. Pin 87 of the relay will connect to the fog lights.
Option 1 - fog lights come on with parkers. Connect pin 86 of the relay to a ground point somewhere (battery negative isn't the greatest idea because it just makes it messy, there are plenty of body bolts in the area).
Option 2 - fog lights can only come on with parkers, but can be switched off. Connect a wire to pin 86 and run this into the cabin, connect it to one side of a switch. Connect the other side of the switch to the ground behind the dash (there are several solid mount points with screws, pick one).