I don't know that it's necessary to tell them, but you can if it makes you feel better. If your stutter's obvious, they're going to find out pretty quick anyway. Earlier on in my career I'd sometimes inform the person I stutter and let me know if they didn't understand anything. I would be careful not to make it sound like an excuse. More of a "Hey, just a heads up, I stutter but it has no impact on my work - let me know if you don't understand something I say, thanks."