Draft: Add lychee to scripts/lint-doc.sh
What does this MR do and why?
Adds lychee to https://gitlab.com/gitlab-org/gitlab/-/blob/master/scripts/lint-doc.sh.
Related technical-writing#979 (closed)
How to set up and validate locally
Numbered steps to set up and validate the change are strongly suggested.
Run locally:
scripts/lint-doc.sh