Clarify that pipeline IDs can be obtained via predefined variables in CI

doc/api/jobs.md

@@ -160,7 +160,7 @@ GET /projects/:id/pipelines/:pipeline_id/jobs
 | Attribute         | Type                           | Required | Description                                                                                                                                                                                                    |
 |-------------------|--------------------------------|----------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
 | `id`              | integer/string                 | yes      | ID or [URL-encoded path of the project](README.md#namespaced-path-encoding) owned by the authenticated user.                                                                                                   |
-| `pipeline_id`     | integer                        | yes      | ID of a pipeline.                                                                                                                                                                                              |
+| `pipeline_id`     | integer                        | yes      | ID of a pipeline. Can also be obtained in CI jobs via the [predefined CI variable](../ci/variables/predefined_variables.md) `CI_PIPELINE_ID`.                                                                                                                                                            |
 | `scope`           | string **or** array of strings | no       | Scope of jobs to show. Either one of or an array of the following: `created`, `pending`, `running`, `failed`, `success`, `canceled`, `skipped`, or `manual`. All jobs are returned if `scope` is not provided. |
 | `include_retried` | boolean                        | no       | Include retried jobs in the response. Defaults to `false`. [Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/272627) in GitLab 13.9.                                                                  |