Adds documentation stating ADO will be gradually enabled on 11.3

doc/topics/autodevops/index.md

@@ -238,6 +238,12 @@ There is also a feature flag to enable Auto DevOps to a percentage of projects
 which can be enabled from the console with
 `Feature.get(:force_autodevops_on_by_default).enable_percentage_of_actors(10)`.
 
+NOTE: **Enabled by default:**
+Starting with GitLab 11.3, the Auto DevOps pipeline will be enabled by default for all
+projects. If it's not explicitly enabled for the project, Auto DevOps will be automatically
+disabled on the first pipeline failure. Your project will continue to use an alternative
+[CI/CD configuration file](../../ci/yaml/README.md) if one is found.
+
 ### Deployment strategy
 
 > [Introduced](https://gitlab.com/gitlab-org/gitlab-ce/issues/38542) in GitLab 11.0.