I noticed no one was able to answer this question, so I just figured it out myself. The addPanel() allows you to pass in one argument to add in a panel into the performance monitor. It is a panel object. The syntax to create a panel object is:
var panel = new Stats.Panel("name", "color1", "color2");
Using this method you can add in a panel as the following:
var panelVar = addPanel( new Stats.Panel( 'name', 'color1', 'color2' ) );
Here is an example:
var fpsPanel = addPanel( new Stats.Panel( 'FPS', '#0ff', '#002' ) );
Next, configuring the panel to show what it wants to show, you have to add-in a your code that configures the panel each frame. To do this you have to run your code in the format panelVar.update(a, b) where a is the amount in the top of the ratio and b is in the bottom. a / b will give the percentage that was shown. You have to run this code between stats.begin() and stats.end() inside the animation frame function.