By Tom Polansek CHICAGO (Reuters) -Archer-Daniels-Midland, one of the world's biggest grain merchants, is offering incentives for U.S. farmers to deliver soybeans to one of its major processing facilities this month as low prices have slowed selling by growers, a grain trader and a company employee with knowledge of the matter said. In an unusual offer during the peak of autumn harvesting, ADM is allowing farmers to deliver soy to its facility in Decatur, Illinois, and set the final sale price later, wit ...