CI: Add a github action that could help to check if links are dead

.404-links.yml

@@ -0,0 +1,2 @@
+delay:
+  'https://github.com': 500 #Avoiding Github rate limit by delaying the request -> 500ms

.github/workflows/404-links.yml

@@ -0,0 +1,14 @@
+name: Dead link checker
+
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    types: [assigned, opened, synchronize, reopened]
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2
+    - name: Check links
+      uses: restqa/404-links@2.2.0