build: add a "yarn build" script to desktop-electron

packages/desktop-electron/package.json

@@ -5,6 +5,7 @@
   "description": "A simple and powerful personal finance system",
   "version": "4.0.2",
   "scripts": {
+    "build": "electron-builder",
     "watch": "cross-env ACTUAL_DOCUMENT_DIR=\"../../data\" ACTUAL_DATA_DIR=\"../../data\" electron ."
   },
   "main": "index.js",