Add StimulusJS and example controller

app/webpacker/controllers/example_controller.js

@@ -0,0 +1,18 @@
+// This is what a basic Stimulus Controller looks like. To apply it to an element you can do:
+// div{"data-controller": "example"}
+// or:
+// div{data: {controller: "example"}}
+
+import { Controller } from "stimulus"
+
+export default class extends Controller {
+  // connect() is a built-in lifecycle callback for Stimulus Controllers. It fires when the
+  // element is loaded on the page, and that also *includes* when some HTML is asynchronously
+  // injected into the DOM. This means initialization is not tied to the page load event, but
+  // will also happen dynamically if and when new DOM elements are added or removed.
+  connect() {
+    console.log("We're connected!")
+  }
+}
+
+// For more info take a look at https://stimulus.hotwired.dev/handbook/introduction