Add Github Action to check for broken links

.github/workflows/link-check.yml

@@ -0,0 +1,12 @@
+name: Check Markdown links
+
+on: [push, pull_request]
+
+jobs:
+  markdown-link-check:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@master
+    - uses: gaurav-nelson/github-action-markdown-link-check@v1
+      with:
+        config-file: 'mlc_config.json'

mlc_config.json

@@ -0,0 +1,5 @@
+{
+  "retryCount": 3,
+  "fallbackRetryDelay": "10s",
+  "aliveStatusCodes": [200, 429]
+}