Updated for 7.0
Click on the Settings icon (the gear) located to the right side of the search bar. This will take you here:
Within the horizontal navigation bar, select Users. Then, Additional Fields. This will take you here:
To add an additional field, click the + Add button in the bottom right-hand corner. A pop-up window will appear that looks like this:
In the pop-up window, follow the prompts to include the demographic name and description.
Click on each box and type in the respective information or select from the drop-down options.
When done, click the Save button located at the bottom of the pop-up window.