* README.md, docs/HACKING.md, man/man1/apropos.man1,
man/man1/lexgrog.man1, man/man1/man-recode.man1, man/man1/man.man1,
man/man1/manconv.man1, man/man1/manpath.man1, man/man1/whatis.man1,
man/man1/zsoelim.man1, man/man5/manpath.man5, man/man8/accessdb.man8,
man/man8/catman.man8, man/man8/mandb.man8: Change GitLab URL to
https://gitlab.com/man-db/man-db.
* NEWS.md: Document this.