react, slinky, esbuild and a readme.

src/main/scala/app/main.scala

@@ -1,13 +1,19 @@
 package app
 
-import org.scalajs.dom
 import org.scalajs.dom.document
+import slinky.web.ReactDOM
+import slinky.web.html._
 
 object Main {
   def main(args: Array[String]): Unit = {
     val div = document.createElement("div")
-    div.id = "main"
+    div.id = "root"
     document.body.appendChild(div)
     println("Hello!")
+
+    ReactDOM.render(
+      h1("Hello, world?"),
+      document.getElementById("root")
+    )
   }
 }