Create subheading for API use

Link to a few APIs helpful for Auto DevOps work.

doc/topics/autodevops/customize.md

@@ -5,7 +5,8 @@ almost everything to fit your needs. Auto DevOps offers everything from custom
 [buildpacks](#custom-buildpacks), to [Dockerfiles](#custom-dockerfile), and
 [Helm charts](#custom-helm-chart). You can even copy the complete
 [CI/CD configuration](#customizing-gitlab-ciyml) into your project to enable
-staging and canary deployments, and more.
+staging and canary deployments,
+[manage Auto DevOps with GitLab APIs](customize.md#extend-auto-devops-with-the-api), and more.
 
 ## Custom buildpacks
 
@@ -77,6 +78,16 @@ Avoid passing secrets as Docker build arguments if possible, as they may be
 persisted in your image. See
 [this discussion of best practices with secrets](https://github.com/moby/moby/issues/13490) for details.
 
+## Extend Auto DevOps with the API
+
+You can extend and manage your Auto DevOps configuration with GitLab APIs:
+
+- [Settings that can be accessed with API calls](../../api/settings.md#list-of-settings-that-can-be-accessed-via-api-calls),
+  which include `auto_devops_enabled`, to enable Auto DevOps on projects by default.
+- [Creating a new project](../../api/projects.md#create-project).
+- [Editing groups](../../api/groups.md#update-group).
+- [Editing projects](../../api/projects.md#edit-project).
+
 ## Forward CI variables to the build environment
 
 > [Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/25514) in GitLab 12.3, but available in versions 11.9 and above.

doc/topics/autodevops/index.md

@@ -104,8 +104,10 @@ knowledge of the following:
 - [GitLab Runner](https://docs.gitlab.com/runner/)
 - [Prometheus](https://prometheus.io/docs/introduction/overview/)
 
-Auto DevOps provides great defaults for all the stages and makes use of [CI templates](https://gitlab.com/gitlab-org/gitlab/-/tree/master/lib/gitlab/ci/templates); you can, however,
-[customize](customize.md) almost everything to your needs.
+Auto DevOps provides great defaults for all the stages and makes use of
+[CI templates](https://gitlab.com/gitlab-org/gitlab/-/tree/master/lib/gitlab/ci/templates). You can, however,
+[customize](customize.md) almost everything to your needs, and
+[manage Auto DevOps with GitLab APIs](customize.md#extend-auto-devops-with-the-api).
 
 For an overview on the creation of Auto DevOps, read more
 [in this blog post](https://about.gitlab.com/blog/2017/06/29/whats-next-for-gitlab-ci/).