Merge branch 'doc-broken-links' into 'master'

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

doc/ci/triggers/README.md

@@ -33,7 +33,7 @@ POST /projects/:id/trigger/builds
 
 The required parameters are the trigger's `token` and the Git `ref` on which
 the trigger will be performed. Valid refs are the branch, the tag or the commit
-SHA. The `:id` of a project can be found by [querying the API](../api/projects.md)
+SHA. The `:id` of a project can be found by [querying the API](../../api/projects.md)
 or by visiting the **Triggers** page which provides self-explanatory examples.
 
 When a rebuild is triggered, the information is exposed in GitLab's UI under

doc/markdown/markdown.md

@@ -402,7 +402,7 @@ There are two ways to create links, inline-style and reference-style.
 
 [I'm a reference-style link][Arbitrary case-insensitive reference text]
 
-[I'm a relative reference to a repository file](LICENSE)
+[I'm a relative reference to a repository file](LICENSE)[^1]
 
 [You can use numbers for reference-style link definitions][1]
 
@@ -594,3 +594,4 @@ By including colons in the header row, you can align the text within that column
 
 [rouge]: http://rouge.jneen.net/ "Rouge website"
 [redcarpet]: https://github.com/vmg/redcarpet "Redcarpet website"
+[^1]: This link will be broken if you see this document from the Help page or docs.gitlab.com