Add docs workflow on Github

.github/workflows/docs.yml

@@ -0,0 +1,26 b''
+name: Run tests
+
+on: [push, pull_request]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v2
+    - name: Set up Python 3.8
+      uses: actions/setup-python@v2
+      with:
+        python-version: 3.8
+    - name: Install Graphviz
+      run: |
+        sudo apt-get update
+        sudo apt-get install graphviz
+    - name: Install Python dependencies
+      run: |
+        python -m pip install --upgrade pip setuptools
+        pip install -r docs/requirements.txt
+    - name: Build docs
+      run: |
+        python tools/fixup_whats_new_pr.py
+        make -C docs/ html SPHINXOPTS="-W"