docs(config): @type ProjectOptions

Add JSDoc: @type for better editor support.

https://www.typescriptlang.org/docs/handbook/jsdoc-supported-types.html

Author: simon04

docs/config/README.md

@@ -22,6 +22,10 @@ The file should export an object containing options:
 
 ``` js
 // vue.config.js
+
+/**
+ * @type {import("@vue/cli-service").ProjectOptions}
+ */
 module.exports = {
   // options...
 }