Add basic workflow with github actions

.github/workflows/python-tests.yml

@@ -0,0 +1,23 @@
+name: Run unit tests
+
+on: [push]
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        python-version: [3.6, 3.7, 3.8, pypy3]
+
+    steps:
+    - uses: actions/checkout@v2
+    - name: Set up Python ${{ matrix.python-version }}
+      uses: actions/setup-python@v2
+      with:
+        python-version: ${{ matrix.python-version }}
+    - name: Install Tox and any other packages
+      run: pip install tox
+    - name: Run Tox
+      # Run tox using the version of Python in `PATH`
+      run: tox -e py