add Github to menu bar

People should know that this great game is something
they can contribute to.

Closes #198

script/engine.js

@@ -171,6 +171,12 @@
 				.text(_('app store.'))
 				.click(function() { window.open('https://itunes.apple.com/us/app/a-dark-room/id736683061'); })
 				.appendTo(menu);
+
+			$('<span>')
+				.addClass('menuBtn')
+				.text(_('github.'))
+				.click(function() { window.open('https://github.com/Continuities/adarkroom'); })
+				.appendTo(menu);
 			
 			// Register keypress handlers
 			$('body').off('keydown').keydown(Engine.keyDown);