You probably don't need to add yeast, but it won't hurt, either.
One option is to use Champagne yeast. It's probably good to add that a few days before you bottle to make sure the yeast won't eat anything the beer yeast didn't. Make sure you're using an actual sparkling wine yeast, and not just a Champagnoise yeast. Not all yeast from Champagne are good for bottling.
The other option is to add a neutral (or the same strain as primary) beer yeast while bottling. I like to use DME to bottle like that, and pitch the yeast like it's a starter a few hours before I'm ready to bottle. It's sort of like speise, which is how Germans traditionally bottled beer.