Create release.yaml

- Create the release.yaml file in the correct directory.
- Trigger the workflow on pull requests merged into the stable branch.

.github/workflows/release.yaml

@@ -0,0 +1,14 @@
+name: Release Workflow
+
+on:
+  push:
+    branches:
+      - stable
+
+jobs:
+  release:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v2
+      # more to come