add GitLab CI job token API authentication section

doc/api/README.md

@@ -77,11 +77,12 @@ authentication is not provided. For
 those cases where it is not required, this will be mentioned in the documentation
 for each individual endpoint. For example, the [`/projects/:id` endpoint](projects.md).
 
-There are three ways to authenticate with the GitLab API:
+There are four ways to authenticate with the GitLab API:
 
 1. [OAuth2 tokens](#oauth2-tokens)
 1. [Personal access tokens](#personal-access-tokens)
 1. [Session cookie](#session-cookie)
+1. [GitLab CI job token](#gitlab-ci-job-token-premium) **(PREMIUM)**
 
 For admins who want to authenticate with the API as a specific user, or who want to build applications or scripts that do so, two options are available:
 
@@ -151,6 +152,14 @@ The primary user of this authentication method is the web frontend of GitLab its
 which can use the API as the authenticated user to get a list of their projects,
 for example, without needing to explicitly pass an access token.
 
+### GitLab CI job token **(PREMIUM)**
+
+With a few API endpoints you can use a [GitLab CI job token](../user/project/new_ci_build_permissions_model.md#job-token)
+to authenticate with the API:
+
+* [Get job artifacts](jobs.md#get-job-artifacts)
+* [Pipeline triggers](pipeline_triggers.md)
+
 ### Impersonation tokens
 
 > [Introduced][ce-9099] in GitLab 9.0. Needs admin permissions.