When you see the folder description text box, make sure WYSIWYG is enabled. You'll know its on when you see all the text options like the bold, italics, and underline thingies above it. Click the "insert image" thingy and you'll have to insert the image link. You can send the pic to yourself through discord then open it in a new tab to copy the address. Or what I did was upload the image to sta.sh (if you have deviantart) and right click to copy the image address. Either works. Hope this helps! I'm not very good at describing things pfff