Add remark check to GHA

.github/workflows/remark.yml

@@ -0,0 +1,24 @@
+name: Remark
+
+on:
+  push:
+    paths:
+    - '**.md'
+  pull_request:
+    paths:
+    - '**.md'
+
+jobs:
+  remark:
+    runs-on: ubuntu-latest
+
+    steps:
+    - name: Checkout
+      uses: actions/checkout@v2.0.0
+    - name: Setup Node.js
+      uses: actions/setup-node@v1.1.0
+    - name: Install remark
+      run: npm install remark-cli remark-lint remark-lint-maximum-line-length remark-preset-lint-recommended
+
+    - name: Check *.md files
+      run: git ls-files -z '*.md' | xargs -0 -n 1 -I {} ./node_modules/.bin/remark {} -u lint -f > /dev/null