Add a basic React implementation of the map.

See client/README.md for instructions.

client/src/index.tsx

@@ -0,0 +1,21 @@
+import React from "react";
+import ReactDOM from "react-dom";
+import "./index.css";
+import App from "./App";
+import { store } from "./app/store";
+import * as serviceWorker from "./serviceWorker";
+import { Provider } from "react-redux";
+
+ReactDOM.render(
+  <React.StrictMode>
+    <Provider store={store}>
+      <App />
+    </Provider>
+  </React.StrictMode>,
+  document.getElementById("root")
+);
+
+// If you want your app to work offline and load faster, you can change
+// unregister() to register() below. Note this comes with some pitfalls.
+// Learn more about service workers: https://bit.ly/CRA-PWA
+serviceWorker.unregister();