Currently it supports two config methods
1: place a chest behind the spawn belt and insert a item in the chest's first slot. You can then remove the chest if you want, the belt will remember.
2: Connect the belt to the circuit network and send a signal over it, the belt will start spawning that item, again you can disconnect after.
Note that switching item type will not clear the belt. If it it backed up you will need to make space to see the effect first.
