From the README:
Copy the contents of src/ to your Inkscape extensions/ folder.
Typical locations include:
* OS X - /Applications/Inkscape.app/Contents/Resources/extensions
* Linux - /usr/share/inkscape/extensions
* Windows - C:\Program Files\Inkscape\share\extensions
* Size and locate your image appropriately:
** The CupCake CNC build platform size is 100mm x 100mm.
** Setting units to mm in Inkscape makes it easy to size your drawing.
** The extension will automatically attempt to center everything.
* Convert all text to paths:
** Select all text objects.
** Choose Path | Object to Path.
* Save as G-Code:
** File | Save a Copy.
** Select MakerBot Unicorn G-Code (*.gcode).
** Save your file.
** For OS X, Pleasant3D is great for this.
** For other operating systems... I don't know!
** Open your .gcode file in ReplicatorG
** Set up your Unicorn and pen.
** Center your build platform.
** Click the Build button!