Add "Build Docs" workflow

.github/workflows/docs.yml

@@ -0,0 +1,40 @@
+name: Build Docs
+
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    strategy:
+        python:
+          - 3.7
+          #- 3.8
+          #- 3.9
+    steps:
+    - name: Check out repository
+      uses: actions/checkout@v2
+      with:
+        # Fetch all commits so that versioneer will return something compatible
+        # with semantic-version
+        fetch-depth: 0
+
+    - name: Set up Python ${{ matrix.python }}
+      uses: actions/setup-python@v2
+      with:
+        python-version: ${{ matrix.python }}
+
+    - name: Install hdf5 (Ubuntu)
+      if: matrix.python == '3.9' && startsWith(matrix.os, 'ubuntu')
+      run: sudo apt-get update && sudo apt-get install -y libhdf5-dev
+
+    - name: Install dependencies
+      run: |
+        python -m pip install --upgrade pip wheel
+        python -m pip install --upgrade tox
+
+    - name: Build docs
+      run: tox -e docs