Add link check action. (#1449)

* Add link check action.

Signed-off-by: Jerome Luckenbach <github@luckenba.ch>

* Add blank line.

Signed-off-by: Jerome Luckenbach <github@luckenba.ch>

.github/workflows/brokenLinkCheck.yml

@@ -0,0 +1,18 @@
+name: Check for broken links
+
+# https://github.blog/2020-08-03-github-actions-improvements-for-fork-and-pull-request-workflows/
+
+on:
+  push:
+    branches:
+    - main
+
+jobs:
+
+  markdown-link-check:
+
+    name: Check for broken links
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@master
+    - uses: gaurav-nelson/github-action-markdown-link-check@v1