There is: https://forums.dolphin-emu.org/Thread-dolphin-custom-textures-info (Maybe this needs a update for the other backends)
Short: Set ConvertHiresTextures in C:\Users\UserName\Documents\Dolphin Emulator\Config\gfx_*.ini to True. Put the textures to the normal place (Load\GameID\*) and play the game while dolphin converts it in the background.
BTW, it seems like it is an old pack; are you sure there is a more recent one?
Short: Set ConvertHiresTextures in C:\Users\UserName\Documents\Dolphin Emulator\Config\gfx_*.ini to True. Put the textures to the normal place (Load\GameID\*) and play the game while dolphin converts it in the background.
BTW, it seems like it is an old pack; are you sure there is a more recent one?