add fly deploy workflow

.github/workflows/fly.yml

@@ -0,0 +1,17 @@
+name: Fly Deploy
+on:
+  push:
+    branches:
+      - master # change to main if needed
+jobs:
+  deploy:
+    name: Deploy app
+    runs-on: ubuntu-latest
+    concurrency: deploy-group # optional: ensure only one action runs at a time
+    steps:
+      - uses: actions/checkout@v3
+      - uses: superfly/flyctl-actions/setup-flyctl@master
+      - run: cd backend # added my me, everything else from https://fly.io/docs/app-guides/continuous-deployment-with-github-actions/
+      - run: flyctl deploy --remote-only
+        env:
+          FLY_API_TOKEN: ${{ secrets.FLY_API_TOKEN }}