add Github workflows

.github/workflows/mardkwon-SEO.yaml

@@ -0,0 +1,22 @@
+name: SEO check
+
+on:
+  push:
+    branches: [ master ]
+
+jobs:
+  seocheck:
+    name: Markdown SEO Check
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+        with:
+          ref: ${{ github.event.pull_request.head.sha }}
+      - name: Markdown SEO Check
+        uses: zentered/markdown-seo-check@v1.1.0
+        with:
+          max_title_length: 70
+          max_description_length: 150
+          max_slug_length: 100
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}