Docs added permissions

Related to: https://gitlab.com/gitlab-org/gitlab/-/issues/29850

doc/ci/merge_request_pipelines/index.md

@@ -13,17 +13,27 @@ changes are pushed to a branch.
 If you want the pipeline to run jobs **only** when merge requests are created or updated,
 you can use *pipelines for merge requests*.
 
-In the UI, these pipelines are labeled as `detached`.
+In the UI, these pipelines are labeled as `detached`. Otherwise, these pipelines appear the same
+as other pipelines.
+
+Any user who has developer [permissions](../../user/permissions.md)
+can run a pipeline for merge requests.
 
 ![Merge request page](img/merge_request.png)
 
-A few notes:
+NOTE: **Note**:
+If you use this feature with [merge when pipeline succeeds](../../user/project/merge_requests/merge_when_pipeline_succeeds.md),
+pipelines for merge requests take precedence over the other regular pipelines.
+
+## Prerequisites
+
+To enable pipelines for merge requests:
 
-- Pipelines for merge requests are incompatible with
-  [CI/CD for external repositories](../ci_cd_for_external_repos/index.md).
-- [Since GitLab 11.10](https://gitlab.com/gitlab-org/gitlab-foss/-/merge_requests/25504), pipelines for merge requests require GitLab Runner 11.9.
-- If you use this feature with [merge when pipeline succeeds](../../user/project/merge_requests/merge_when_pipeline_succeeds.md),
-  pipelines for merge requests take precedence over the other regular pipelines.
+- You must have maintainer [permissions](../../user/permissions.md).
+- Your repository must be a GitLab repository, not an
+  [external repository](../ci_cd_for_external_repos/index.md).
+- [In GitLab 11.10 and later](https://gitlab.com/gitlab-org/gitlab-foss/-/merge_requests/25504),
+  you must be using GitLab Runner 11.9.
 
 ## Configuring pipelines for merge requests
 

doc/ci/merge_request_pipelines/pipelines_for_merged_results/index.md

@@ -34,14 +34,18 @@ In these cases, the pipeline runs as a [pipeline for merge requests](../index.md
 and is labeled as `detached`. If these cases no longer exist, new pipelines will
 again run against the merged results.
 
-## Requirements and limitations
+Any user who has developer [permissions](../../../user/permissions.md) can run a
+pipeline for merged results.
 
-Pipelines for merged results have the following requirements and limitations:
+## Prerequisites
 
-- Pipelines for merged results require [GitLab Runner](https://gitlab.com/gitlab-org/gitlab-runner) 11.9 or newer.
-- Forking/cross-repo workflows are not currently supported. To follow progress,
+To enable pipelines for merge results:
+
+- You must have maintainer [permissions](../../../user/permissions.md).
+- You must be using [GitLab Runner](https://gitlab.com/gitlab-org/gitlab-runner) 11.9 or later.
+- You must not be forking or using cross-repo workflows. To follow progress,
   see [#11934](https://gitlab.com/gitlab-org/gitlab/issues/11934).
-- This feature is not available for
+- You must not be using
   [fast forward merges](../../../user/project/merge_requests/fast_forward_merge.md) yet.
   To follow progress, see [#58226](https://gitlab.com/gitlab-org/gitlab/-/issues/26996).
 

doc/ci/merge_request_pipelines/pipelines_for_merged_results/merge_trains/index.md

@@ -30,6 +30,14 @@ If the pipeline for the merge request at the front of the train completes succes
 the changes are merged into the target branch, and the other pipelines continue to
 run.
 
+To add a merge request to a merge train, you need [permissions](../../../../user/permissions.md) to push to the target branch.
+
+NOTE: **Note:**
+Each merge train can run a maximum of **twenty** pipelines in parallel.
+If more than twenty merge requests are added to the merge train, the merge requests
+will be queued until a slot in the merge train is free. There is no limit to the
+number of merge requests that can be queued.
+
 ## Merge train example
 
 Three merge requests (`A`, `B` and `C`) are added to a merge train in order, which
@@ -55,16 +63,13 @@ Watch this video for a demonstration on [how parallel execution
 of Merge Trains can prevent commits from breaking the default
 branch](https://www.youtube.com/watch?v=D4qCqXgZkHQ).
 
-## Requirements and limitations
+## Prerequisites
 
-Merge trains have the following requirements and limitations:
+To enable merge trains:
 
-- Merge trains require [GitLab Runner](https://gitlab.com/gitlab-org/gitlab-runner) 11.9 or newer.
-- GitLab 12.0 and later requires [Redis](https://redis.io/) 3.2 or higher.
-- Each merge train can run a maximum of **twenty** pipelines in parallel.
-  If more than twenty merge requests are added to the merge train, the merge requests
-  will be queued until a slot in the merge train is free. There is no limit to the
-  number of merge requests that can be queued.
+- You must have maintainer [permissions](../../../../user/permissions.md).
+- You must be using [GitLab Runner](https://gitlab.com/gitlab-org/gitlab-runner) 11.9 or later.
+- In GitLab 12.0 and later, you need [Redis](https://redis.io/) 3.2 or later.
 
 ## Enable merge trains