add optional config for postCmd

config.js

@@ -0,0 +1,17 @@
+'use strict';
+
+const configPath = require('xdg').basedir.configPath('switchmon/config.json');
+
+const defaults = {
+    postCmd: undefined,
+};
+
+let config = Object.assign({}, defaults);
+
+try {
+    config = Object.assign(config, require(configPath));
+} catch(err) {
+    // No config found in "${configPath}". Using defaults...
+}
+
+module.exports = config;