update docs for standalone

[yurii-github]

Version

3.1.3

Reproduction link

https://router.vuejs.org/guide/#javascript

Steps to reproduce

1. read docs https://router.vuejs.org/guide/#javascript
2. try with vue-loader with single-file component approach (by moving each page component to its file)
3. see error "Failed to mount component: template or render function not defined."
4. make ES6 fixes by adding ".default"
   profit

## index.js

import Vue from 'vue'
import VueRouter from 'vue-router'
import App from './App.vue'

Vue.use(VueRouter)

const router = new VueRouter({
  routes: [
    {path: '/', component: require('./pages/Index.vue').default},
    {path: '/about', component: require('./pages/About.vue').default}
  ]
})

window.app =  new Vue({
  router,
  render: h => h(App)
}).$mount('#app')

What is expected?

docs must have solution for standalone approach when vue compiler IS NOT bundled to webbrowser

What is actually happening?

you don't have such docs, instead you have ton of closed unresolved issues from clients, example:

#824

vuejs/vue-cli#1875

#794

#713

and so on. internet is flooded with this stuff

[posva]

Impactful contributions to docs are welcomed. In this case though, having to use .default is unrelated to vue, vue-router, or vue's compiler, it's part of the bundler being used and the way the component is exported (module.exports vs export default)