chore: replace linkcheck by lychee (#282)

.woodpecker/docs.yml

@@ -8,17 +8,25 @@ when:
 steps:
   markdownlint:
     image: quay.io/thegeeklab/markdownlint-cli
+    group: test
     commands:
       - markdownlint 'README.md' 'CONTRIBUTING.md'
 
   spellcheck:
     image: quay.io/thegeeklab/alpine-tools
+    group: test
     commands:
       - spellchecker --files '_docs/**/*.md' 'README.md' 'CONTRIBUTING.md' -d .dictionary -p spell indefinite-article syntax-urls
     environment:
       FORCE_COLOR: "true"
       NPM_CONFIG_LOGLEVEL: "error"
 
+  link-validation:
+    image: docker.io/lycheeverse/lychee
+    group: test
+    commands:
+      - lychee --no-progress --format detailed README.md
+
   pushrm-dockerhub:
     image: docker.io/chko/docker-pushrm:1
     secrets: