Fix broken documentation links

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/15249

- [x] `/help/ui`- This is working for me
- [x] `/help/ci/examples/deployment/README.md` - Fixed
- [x] `/help/ci/api/projects.md` - Fixed
- [x] `/help/markdown/LICENSE` - Cannot do much to fix it, added a note.
- [x] `/help/ci/ssh/README.md` - Cannot find this link referenced anywhere.

See merge request !3903