Hello,
As you said, just simply tie off the grommet on the head of the jib to the forestay with a small length of rope.
You could see in this video the small black rope that comes with the boat.
https://www.youtube.com/watch?v=VWBSySwXRtAAs for tension, I just connected the forestay to the front crossbar and the mast, while the mast is laying horizontally on the boat with someone pushing the mast base to keep the forestay wire tensioned, so I could tie the rope with little tension with Half Hitches to the forestay wire.