doc: 添加文档

src/App.js

@@ -1,8 +1,13 @@
+import { useEffect } from "react";
 import Editor from "./view/Editor";
 import globalStore, { GlobalContext } from "./store/global";
+import { loadExample } from "./util/load-example";
 
 // ENHANCE: 替换掉antd组件库。。一堆莫名其妙的毛病
 function App() {
+  useEffect(() => {
+    loadExample();
+  }, []);
   return (
     <GlobalContext.Provider value={globalStore}>
       <Editor></Editor>