The note that you've found appears to be a receipt for the suppression traps surrounding the lair of Broodlord Lashlayer. The note states that if the Broodlord needs more Suppression Traps, he can purchase them from the camp of the seller, near the west side of the Burning Steppes, just south of the road to the Altar of Storms. The note also says that the seller may be moving on soon, so the Broodlord should hurry if he wants more traps.