actions: add workflow for publishing docs

.github/workflows/docs.yml

@@ -0,0 +1,28 @@
+name: Publish docs
+
+on:
+  push:
+    branches:
+      - main
+  workflow_dispatch: {}
+
+jobs:
+  docs:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - name: Setup Python
+        uses: actions/setup-python@v2
+        with:
+          python-version: 3.9
+      - name: Install system dependencies
+        run: sudo apt-get install -y libkrb5-dev
+      - name: Install Tox
+        run: pip install tox
+      - name: Run Tox
+        run: tox -e docs
+      - name: Publish
+        uses: JamesIves/github-pages-deploy-action@4.1.3
+        with:
+          branch: gh-pages
+          folder: docs/_build/html