The wiki is pretty straighforward but those options are not present when I follow the steps in the wiki. I select this:
System --> Settings --> AddOns
All I see is a list of add ons like Youtube and Railscasts. There's no option for installing from a zip file like the wiki says. Pressing ".." just takes me to the list of AddOn types like "Album Information" and "Artist Information" etc.
The wiki looks to be out of date.