Add markdownlint-cli2 as Github Action and pre-commit hook

.github/workflows/pr.yaml

@@ -0,0 +1,17 @@
+on: [pull_request]
+
+permissions:
+  contents: read
+  pull-requests: read
+  checks: write
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  lint:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4
+    - uses: DavidAnson/markdownlint-cli2-action@v17