BUILD & ISNTALL INSTRUCTIONS, SPECIFICS
Now build and run the project. The resulting MonoDevelop.ThemeEditor.dll is your addin. To run it, find the addins directory. The location is dependent on the OS:
Mac ~/Library/Application Support/XamarinStudio-4.0/LocalInstall/Addins Windows Vista/7 ~/AppData/Local/XamarinStudio-4.0/LocalInstall/Addins Linux ~/.local/share/MonoDevelop-4.0/LocalInstall/Addins