add playground

playground/counter.tsx

@@ -0,0 +1,12 @@
+import * as React from "react"
+import { Button } from "../src/main.js"
+
+export function Counter() {
+  const [count, setCount] = React.useState(0)
+  return (
+    <>
+      this button was clicked {count} times
+      <Button onClick={() => setCount(count + 1)}>clicc</Button>
+    </>
+  )
+}