By Alek Arend The San Francisco 49ers added some depth at the wide receiver position today. Per NFL insider Field Yates, the 49ers have signed veteran wide receiver Marcus Johnson. Johnson, a former Texas standout, has been in the NFL for five years. He’s played for three teams – the Eagles, Colts and Titans – during that span. The 6-foot-1 wideout has 51 catches for 839 yards and three touchdowns for his career. Johnson now heads to San Francisco. He should provide some nice depth for the 49ers’ offensive attack this upcoming season. Although this is a nice signing by the 49ers, it’s not the …