Guild Launch sites can use the XML from in-game commands to get you a file you can upload to add everyone to the site automatically, instead of having to update everything by hand.
Step One: Getting the XML
The first step is to actually get the XML. This is done in-game with a simple command: /dumpguild
Using that will generate a guild.xml file in the install directory for Rift, which you can then use to upload the information to your site.
Step Two: The Import
Once you have the guild.xml file from your install directory, go to the Roster tab of your Guild Launch site (NOT on the Admin section). There will be a link under 'Roster Navigation' on the left of the Guild Roster page which you can click to get to the full XML import option.
From here, you will see the following screen:
Choose your Faction (Defiant or Guardian) from the dropdown menu, then copy and paste the XML from the guild.xml file on your computer to the 'Guild.xml File Contents' field. Click 'Run Guild XML Import' and you're done - the system does the rest!