Add CI step to check for documentation updates

.github/workflows/check_docs.yml

@@ -0,0 +1,28 @@
+name: Check Documentation
+
+on:
+  push:
+    branches:
+    - main
+  pull_request:
+    branches:
+    - main
+
+jobs:
+  check-docs:
+    runs-on: ubuntu-latest
+    steps:
+    - name: Checkout code
+      uses: actions/checkout@v2
+
+    - name: Setup Python
+      uses: actions/setup-python@v2
+      with:
+        python-version: 3.8
+
+    - name: Install dependencies
+      run: |
+        pip install -r requirements.txt
+
+    - name: Check for documentation updates
+      run: ./scripts/check_docs.sh

ci/check_docs.sh

@@ -0,0 +1,8 @@
+set -e
+
+if git diff --quiet HEAD^ HEAD -- docs/; then
+  echo "Documentation has not been updated."
+  exit 1
+else
+  echo "Documentation is up-to-date."
+fi