Add a GH action for the link checker

.github/workflows/links.yml

@@ -0,0 +1,22 @@
+name: Check if all links are reachable
+on:
+  push:
+    branches: main
+  pull_request:
+    branches: main
+  workflow_dispatch:
+
+jobs:
+  check:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Use Node.js
+        uses: actions/setup-node@v3
+        with:
+          node-version: '18'
+      - name: Checkout
+        uses: actions/checkout@v3
+      - name: Install
+        run: npm install
+      - name: Check links
+        run: npm run check:links