Add 'Basic Usage' part to README

[QuadDamn]

I'd like to recommend that you guys add a Basic Usage section to the README to help folks.

This is my recommendation:

---

Basic Usage

HTML inside of Vue template file:

<template>
  <div id="app">
    <formio src="" url="" form="" submission="" options="" v-on:submit=""></formio>
  </div>
</template>

Javascript inside of Vue template file.

<script>

  import FormIo from 'vue-formio';

  export default {

      name: 'app',
      components: { FormIo },
  }
</script>

[randallknutson]

Done a while ago.