Add info about system-wide disable

doc/ci/pipelines.md

@@ -470,12 +470,13 @@ To illustrate its life cycle:
 1. When the pipeline finished, its persistent ref is cleaned up in a background process.
 
 NOTE: **NOTE**: At this moment, this feature is on by default and can be manually disabled
-by disabling `depend_on_persistent_pipeline_ref` feature flag. If you'd be interested in
+by disabling `depend_on_persistent_pipeline_ref` feature flag. If you're interested in
 manually disabling this behavior, please ask the administrator
 to execute the following commands in rails console.
 
 ```shell
 > sudo gitlab-rails console                                        # Login to Rails console of GitLab instance.
 > project = Project.find_by_full_path('namespace/project-name')    # Get the project instance.
-> Feature.disable(:depend_on_persistent_pipeline_ref, project)     # Disable the feature flag.
+> Feature.disable(:depend_on_persistent_pipeline_ref, project)     # Disable the feature flag for specific project
+> Feature.disable(:depend_on_persistent_pipeline_ref)              # Disable the feature flag system-wide
 ```