Add link checker (#178)

.github/workflows/links.yml

@@ -0,0 +1,19 @@
+name: Markdown Links Check
+
+# runs every monday at 9 am
+on:
+  # push:
+  #   branches:
+  #     - main
+  schedule:
+    - cron: "0 0 1 * *"
+
+jobs:
+  markdown-link-check:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@master
+      - uses: gaurav-nelson/github-action-markdown-link-check@v1
+        with:
+          use-quiet-mode: "yes"
+          use-verbose-mode: "yes"