main: don't ignore config value for single instance mode. allow override using cli param

Fixes: #17

main.cpp

@@ -37,6 +37,7 @@ int main(int argc, char *argv[])
 		QCommandLineParser parser;
 		parser.addOptions({
 			{"new-instance", "Launch a new instance, ignoring any running ones"},
+			{"kill-instances", "Kill all running instances"},
 			{"config", "Use supplied config dir instead of default"},
 		});
 		parser.addHelpOption();