cjxl: add more examples, improve description - #23003

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: tldr-pages/tldr-labeler-action@7cb29444b818130fe056b7e7b3dedcc7db93af45. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/