add readme and GitHub action files

.github/workflows/cleanup.yaml

@@ -0,0 +1,20 @@
+name: Cleanup Koyeb application
+
+on:
+  delete:
+    branches:
+      - '*'
+
+jobs:
+  cleanup:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Install and configure the Koyeb CLI
+        uses: koyeb-community/install-koyeb-cli@v2
+        with:
+          api_token: "${{ secrets.KOYEB_EXAMPLES_APPS_TOKEN }}"
+
+      - name: Cleanup Koyeb application
+        uses: koyeb/action-git-deploy/cleanup@v1
+        with:
+          app-name: spring-boot-${{ github.event.ref }}