add_inventory: Inject Inventory At Plant
In milumtextiles/itemsim: Simulate Linen Rental

Inject new inventory at the plant with the given tagging ratio.

1	add_inventory(state, item, amount, at_time, inject_percent, scan_prob = 1)

`state`	current simulation state to modify
`item`	item number to add inventory for
`amount`	quantity of inventory to add
`at_time`	time stamp to add the new inventory at
`inject_percent`	tag the new inventory at this percentage
`scan_prob`	probability of the tags being scanned