Add workflow to automatically publish to PyPI

.github/workflows/publish.yaml

@@ -0,0 +1,35 @@
+name: Publish to PyPI
+
+on:
+  release:
+    types: [published]
+
+jobs:
+  deploy:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v2
+
+      # Make sure tags are fetched, so we can get a version.
+      - run: |
+          git fetch --prune --unshallow --tags
+
+      - name: Set up Python
+        uses: actions/setup-python@v2
+        with:
+          python-version: "3.9"
+
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          python -m pip install --upgrade build twine
+
+      - name: Build and publish
+        env:
+          TWINE_USERNAME: ${{ secrets.PYPI_USERNAME }}
+          TWINE_PASSWORD: ${{ secrets.PYPI_PASSWORD }}
+
+        run: |
+          python -m build
+          twine upload dist/*