Auto check missing / forbidden external papers and raise issue (#624)

* Create lychee.yml
* Link checker with auto create issue
* 📅 run once a month

Request from https://github.com/papers-we-love/papers-we-love/pull/624#issuecomment-939320960

.github/workflows/lychee.yml

@@ -0,0 +1,28 @@
+name: lychee
+
+on:
+  push:
+  pull_request:
+  schedule:
+    - cron: '0 0 1 * *'
+
+jobs:
+  links:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2.3.4
+   
+    - name: Link Checker
+      uses: lycheeverse/lychee-action@master
+      #env:
+      #  GITHUB_TOKEN: ${{secrets.GITHUB_TOKEN}}
+      with:
+        args: '--verbose --no-progress **/*.md'
+
+    - name: Create Issue From File
+      uses: peter-evans/create-issue-from-file@v2
+      with:
+        title: Link Checker Report
+        content-filepath: ./lychee/out.md
+        labels: report, automated issue
+