Add docs for scheduled pipeline variables

See https://gitlab.com/gitlab-org/gitlab-ce/issues/32568

doc/ci/variables/README.md

@@ -9,7 +9,7 @@ and a list of **user-defined variables**.
 The variables can be overwritten and they take precedence over each other in
 this order:
 
-1. [Trigger variables][triggers] (take precedence over all)
+1. [Trigger variables][triggers] or [scheduled pipeline variables](../../user/project/pipelines/schedules#making-use-of-scheduled-pipeline-variables) (take precedence over all)
 1. [Secret variables](#secret-variables) or [protected secret variables](#protected-secret-variables)
 1. YAML-defined [job-level variables](../yaml/README.md#job-variables)
 1. YAML-defined [global variables](../yaml/README.md#variables)

doc/user/project/pipelines/schedules.md

@@ -31,6 +31,15 @@ is installed on.
 
 ![Schedules list](img/pipeline_schedules_list.png)
 
+### Making use of scheduled pipeline variables
+
+> [Introduced][ce-12328] in GitLab 9.4.
+
+You can pass any number of arbitrary variables and they will be available in
+GitLab CI so that they can be used in your `.gitlab-ci.yml` file.
+
+![Scheduled pipeline variables](img/pipeline_schedule_variables.png)
+
 ## Using only and except
 
 To configure that a job can be executed only when the pipeline has been
@@ -79,4 +88,5 @@ don't have admin access to the server, ask your administrator.
 
 [ce-10533]: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/10533
 [ce-10853]: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/10853
+[ce-12328]: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/12328
 [settings]: https://about.gitlab.com/gitlab-com/settings/#cron-jobs