Add docs

docs/src/.vuepress/enhanceApp.js

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+/**
+ * Client app enhancement file.
+ *
+ * https://v1.vuepress.vuejs.org/guide/basic-config.html#app-level-enhancements
+ */
+
+export default ({
+  Vue, // the version of Vue being used in the VuePress app
+  options, // the options for the root Vue instance
+  router, // the router instance for the app
+  siteData // site metadata
+}) => {
+  // ...apply enhancements for the site.
+}