add node for doc testing

.github/workflows/testing.yml

@@ -12,11 +12,16 @@ jobs:
       uses: actions/setup-python@v4
       with:
         python-version: ${{ matrix.python-version }}
+    - name: Setup Node
+      uses: actions/setup-node@v1
+      with:
+        node-version: '16'
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip
         pip install -r tests-requirements.txt
         pip install -r requirements.txt
+        npm install -g remark-cli remark-validate-links
     - name: Run sequential tests
       run: |
         ./tests.sh