The easiest option is just to have HeaderController configured to open with multiple links (so that once they click on "About/Help" they get options to click for a help page, or basic info about the map, or metadata, or whatever).
Otherwise you would need to edit HeaderControllerWidget.mxml, and near the bottom copy/paste the link hbox. You would then either need to manually type in the content you want to serve, or modify your xml file to have two sets of data, and the mxml to be able to parse them out separately and put each one in its own linkbox.
