Dice Roller Help
There's no need to put it in the dice string, because the options are already in place lower down.
If you look a little farther down on that Help page, you'll find some instructions for placing Dice Roller links in text. There, you can set the dice to roll, the game system, and options like rerolling and dropping/keeping dice. It's especially helpful to use this on character sheets -- in the places where you have a die-roll bonus or number of dice listed, substitute that part with a formatted link to the die roller.
For instance, in a d20-based game, you might have a spot on your sheet that says
Initiative +2
If, instead, you make it say
Initiative [dice=1d20+2 memo="Initiative" text="+2"]
You'll see the same text, but the "+2" will be a link that pops up the die roller with everything filled in.