See http://www.minecraftforum.net/forums/mapping-and-modding/minecraft-mods/2469613 for more information.

This project is licensed under the MIT license. Please read the LICENSE file for more information.

First, download and install Liteloader, available from:
Then, press Windows-R, then type/paste:
%APPDATA%/.minecraft/mods
in the text box, then hit enter.
After that, you can drag the .litemod file you downloaded into the folder.