It does this by default. For instance if you choose the "Single Infusion, Medium Body" mash profile, then examine the brewsheet instructions (either using the Preview Brewsheet button, or backing out of the recipe details to the My Recipes list and changing the preview mode in the toolbar from Classic or Normal to one of the brewsheet options), this will show the sparge volume and temps.
To have the recommended volume calculation work right, you need to make sure you configure your equipment sizes properly, then select the right equipment for that recipe.