add github action to check markdown

Author: Remi-Gau

.github/workflows/check_markdown.yml

@@ -0,0 +1,31 @@
+name: Check Markdown
+
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+    branches: '*'
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+
+    steps:
+
+    - uses: actions/checkout@v2
+      with:
+        submodules: true
+        fetch-depth: 1
+
+    - uses: actions/setup-node@v2
+      with:
+        node-version: '10'
+
+    - name: Install dependencies and checkmarkdown
+      run: |
+        npm install `cat npm-requirements.txt`
+        remark . --frail
+
+