Add GH Action to deploy documentation (#8)

.github/workflows/documentation.yml

@@ -0,0 +1,25 @@
+name: Update documentation
+
+on:
+  push:
+    branches:
+      - master
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v1
+    - name: Set up Python 3.7
+      uses: actions/setup-python@v1
+      with:
+        python-version: 3.7
+    - name: Install dependencies
+      run: |
+        python -m pip install --upgrade pipenv
+        pipenv install --dev
+    - name: Build and deploy documentation
+      run: |
+        pipenv run mkdocs gh-deploy