Added notes around limitations depending on target

Related to https://gitlab.com/groups/gitlab-org/-/epics/2068

doc/topics/autodevops/index.md

@@ -88,6 +88,9 @@ in multiple ways:
 
 ## Features
 
+NOTE:
+Depending on your target platform, some features might not be available to you.
+
 Comprised of a set of [stages](stages.md), Auto DevOps brings these best practices to your
 project in a simple and automatic way:
 

doc/topics/autodevops/stages.md

@@ -11,6 +11,9 @@ Read them carefully to understand how each one works.
 
 ## Auto Build
 
+NOTE:
+Auto Build is not supported if Docker in Docker is not available for your GitLab Runners, like in OpenShift clusters. GitLab's OpenShift support is tracked [in a dedicated epic](https://gitlab.com/groups/gitlab-org/-/epics/2068).
+
 Auto Build creates a build of the application using an existing `Dockerfile` or
 Heroku buildpacks. The resulting Docker image is pushed to the
 [Container Registry](../../user/packages/container_registry/index.md), and tagged