Merge branch 'patch-3' into 'master'

Fix documentation of gitlab-ci's `when` keyword.

## What does this MR do?

Fixes description of the `when` keyword in the Jobs keywords description table.

## Does this MR meet the acceptance criteria?

- [ ] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [ ] API support added
- Tests
  - [ ] Added for this feature/bug
  - [ ] All builds are passing
- [ ] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [ ] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5868

doc/ci/yaml/README.md

@@ -353,7 +353,7 @@ job_name:
 | except        | no | Defines a list of git refs for which build is not created |
 | tags          | no | Defines a list of tags which are used to select Runner |
 | allow_failure | no | Allow build to fail. Failed build doesn't contribute to commit status |
-| when          | no | Define when to run build. Can be `on_success`, `on_failure` or `always` |
+| when          | no | Define when to run build. Can be `on_success`, `on_failure`, `always` or `manual` |
 | dependencies  | no | Define other builds that a build depends on so that you can pass artifacts between them|
 | artifacts     | no | Define list of build artifacts |
 | cache         | no | Define list of files that should be cached between subsequent runs |