Add missing actions/checkout to markdown check

Author: Sh3Rm4n

.github/workflows/ci.yml

@@ -148,10 +148,12 @@ jobs:
     name: Markdown Lint
     runs-on: ubuntu-latest
     steps:
+      - uses: actions/checkout@v2
       - uses: nosborn/[email protected]
         with:
           files: .
-          ignore_files: "target/"
+          config_file: .markdownlint.yml
+          ignore_files: target/
 
   link-checker:
     name: Link Checker