add markdown link checker for PRs

Author: pthmas

.github/workflows/markdowd_link_checker.yml

@@ -0,0 +1,18 @@
+name: Check Markdown links
+
+on: 
+  # This workflow requires pull_request and won't work with pull_request_target 
+  # due to github permissions 
+  pull_request:
+    types:
+      - opened
+      - reopened
+      - synchronize
+      - closed
+
+jobs:
+  markdown-link-check:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4
+    - uses: tcort/github-action-markdown-link-check@v1