Add CI action to check links in README

.github/workflows/check-links.yaml

@@ -0,0 +1,22 @@
+name: Check links in markdown
+
+on: push
+
+jobs:
+  convert_via_pandoc:
+    runs-on: ubuntu-22.04
+    steps:
+      - uses: actions/checkout@v3
+      - name: List files
+        run: ls -la
+      - uses: docker://pandoc/core:2.9
+        with:
+          args: >- # allows you to break string into multiple lines
+            --standalone
+            --from markdown
+            --output=readme.html
+            README.md
+      - name: Run htmltest
+        uses: wjdp/htmltest-action@master
+        with:
+          path: readme.html