extract the content of the .zip file inside plugins/ItemsAdder folder
use the command /iazip
(upload the pack on Dropbox if you're using Dropbox and update the config.yml url, then use /iareload to reload the config.yml)
use the command /credits
To edit the text edit the file: plugins\ItemsAdder\data\resource_pack\assets\minecraft\texts\end.txt
To edit the logo edit the file: plugins\ItemsAdder\data\resource_pack\assets\minecraft\textures\gui\title\minecraft.png (you must split the logo in half like I did, very PRECISELY)