The 49ers have signed sixth-round wide receiver Kyle Williams to a four-year contract. It’s worth $1.86 million and includes a $79,400 signing bonus, according to a league source. Williams received a 3.3 percent increase over last year’s slot. Williams received base salaries of $320,000, $405,000, $490,000 and $575,000. He caught 57 passes for 815 yards and eight touchdowns as a senior.