add react and typescript

app/javascript/packs/application.ts

@@ -0,0 +1,15 @@
+// This file is automatically compiled by Webpack, along with any other files
+// present in this directory. You're encouraged to place your actual application logic in
+// a relevant structure within app/javascript and only use these pack files to reference
+// that code so it'll be compiled.
+
+// import Rails from "@rails/ujs"
+// import Turbolinks from "turbolinks"
+// import * as ActiveStorage from "@rails/activestorage"
+// import "channels"
+
+// Rails.start()
+// Turbolinks.start()
+// ActiveStorage.start()
+
+import './src/index'