I've created an SVG icon for the game. It should resemble a miner's lamp. :-)
Feel free to use it instead of "lamp.png". There's also a .desktop file for the program. In order to make use of it, the .desktop file should be installed into $(PREFIX)/usr/share/applications/advent.desktop.
The icon is expected at $(PREFIX)/usr/share/icons/hicolor/scalable/apps/advent.svg.