U.S. companies added jobs at the slowest pace in three years in April, a private survey found, a sign that slower growth and volatile financial markets could weigh on hiring. Payroll processor ADP said Wednesday that businesses added 156,000 jobs in April, down from 194,000 in March. Manufacturers shed 11,000 jobs, after losing 3,000 the previous month. Services firms added 166,000, down from 189,000. The slowdown was also driven by weaker hiring at medium and larger companies. Small businesses added jobs at the same pace as previous months. …