Oh yeah thanks for asking. Not sure about a guide, but if you open the game and open a customization menu for a character you should get a button that is called "Select Custom Portrait" and then if you click that you will get a menu where one button is labeled "Open system folder." Once you click that it will take you to a directory somewhere that has a few directories in it (including saves, etc). The mods need to go into the "mods" directory there, and the portraits, exposed etc. folders inside the image zip need to go directly into that top level directory (so the portraits folder and so on should be at the same level as saves, not inside the directory they probably come out the zip in). Iirc the mods folder exists by default, portraits and bodies folders might exist as well? But you should be able to just overwrite them with what is in the zip.