Add the release workflow

It has to be triggered manually for now.

.github/workflows/release.yml

@@ -0,0 +1,28 @@
+name: Release
+
+on:
+  # Add a "Trigger" button to manually start the workflow.
+  workflow_dispatch:
+    inputs:
+      branch:
+        description: "The branch, tag or SHA to release from"
+        required: true
+        default: "master"
+  # It could be fully automated by uncommenting following lines.
+  # Let's see later if we are confident enough to try it :)
+  # release:
+  #   types:
+  #     - published
+
+jobs:
+  new-release:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions/setup-python@v2
+        with:
+          python-version: 3.9
+      - run: make publish
+        env:
+          TWINE_USERNAME: __token__
+          TWINE_PASSWORD: ${{ secrets.PYPI_TOKEN }}