message: docs(add-this): update usage
diff: @@ -49,8 +49,10 @@ npm i -D vuepress-plugin-add-this@next
  ```ts
  // .vuepress/config.ts
  +import { addThis } from "vuepress-plugin-add-this";
  +
  export default {
  - plugins: [["add-this", { pubid: "your pubid" }]],
  + plugins: [addThis({ pubid: "your pubid" })],
  };
  ```
  @@ -60,8 +62,10 @@ export default {
  ```js
  // .vuepress/config.js
  +const { addThis } = require("vuepress-plugin-add-this");
  +
  module.exports = {
  - plugins: [["add-this", { pubid: "your pubid" }]],
  + plugins: [addThis({ pubid: "your pubid" })],
  };
  ```
  