DiiLC is a simple application to download and insert the DLC (downloadable content) or HDLC (hacked downloadable content) into Animal Crossing City Folk savegame file (use Waninkoko's savegame extractor for extracting savegame file)
I don't have a wii u anymore to test it myself, but if homebrews are not visible on the wii u menu I think you can press L + R + minus to open the plugin menu, there should be an option called "homebrews on wii u menu" or something similar