Added Enable instructions

Related to https://gitlab.com/gitlab-org/gitlab/-/issues/213293

doc/api/merge_requests.md

@@ -904,7 +904,7 @@ The new pipeline can be:
 
 - A detached merge request pipeline.
 - A [pipeline for merged results](../ci/merge_request_pipelines/pipelines_for_merged_results/index.md)
-  if the [project setting is enabled](../ci/merge_request_pipelines/pipelines_for_merged_results/index.md#enabling-pipelines-for-merged-results).
+  if the [project setting is enabled](../ci/merge_request_pipelines/pipelines_for_merged_results/index.md#enable-pipelines-for-merged-results).
 
 ```plaintext
 POST /projects/:id/merge_requests/:merge_request_iid/pipelines

doc/ci/merge_request_pipelines/index.md

@@ -7,9 +7,8 @@ last_update: 2019-07-03
 
 > [Introduced](https://gitlab.com/gitlab-org/gitlab-foss/issues/15310) in GitLab 11.6.
 
-In a [basic configuration](../pipelines/pipeline_architectures.md), GitLab runs a pipeline each time
-changes are pushed to a branch. The settings in the [`.gitlab-ci.yml`](../yaml/README.md)
-file, including `rules`, `only`, and `except`, determine which jobs are added to a pipeline.
+In a [basic configuration](../pipelines/pipeline_architectures.md#basic-pipelines), GitLab runs a pipeline each time
+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*.
@@ -28,7 +27,7 @@ A few notes:
 
 ## Configuring pipelines for merge requests
 
-To configure pipelines for merge requests, configure your CI yaml file.
+To configure pipelines for merge requests, configure your [CI/CD configuration file](../yaml/README.md).
 There are a few different ways to do this.
 
 ### Enable pipelines for merge requests for all jobs

doc/ci/merge_request_pipelines/pipelines_for_merged_results/index.md

@@ -36,31 +36,41 @@ again run against the merged results.
 
 ## Requirements and limitations
 
-Pipelines for merged results require a [GitLab Runner][runner] 11.9 or newer.
-
-[runner]: https://gitlab.com/gitlab-org/gitlab-runner
-
-In addition, pipelines for merged results have the following limitations:
+Pipelines for merged results have the following requirements and limitations:
 
+- 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,
   see [#11934](https://gitlab.com/gitlab-org/gitlab/issues/11934).
 - This feature is not available for
   [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).
 
-## Enabling Pipelines for Merged Results
+## Enable pipelines for merged results
 
-To enable pipelines on merged results at the project level:
+To enable pipelines for merged results for your project:
 
+1. [Configure your CI/CD configuration file](../index.md#configuring-pipelines-for-merge-requests)
+   so that the pipeline or individual jobs run for merge requests.
 1. Visit your project's **Settings > General** and expand **Merge requests**.
 1. Check **Merge pipelines will try to validate the post-merge result prior to merging**.
-1. Click **Save changes** button.
+1. Click **Save changes**.
+
+CAUTION: **Caution:**
+If you select the check box but don't configure your CI/CD to use
+pipelines for merge requests, your merge requests may become stuck in an
+unresolved state or your pipelines may be dropped.
+
+## Using Merge Trains
 
-![Merge request pipeline config](img/merge_request_pipeline_config.png)
+When you enable [Pipelines for merged results](#pipelines-for-merged-results-premium),
+GitLab [automatically displays](merge_trains/index.md#add-a-merge-request-to-a-merge-train)
+a **Start/Add Merge Train button**.
 
-CAUTION: **Warning:**
-Make sure your `gitlab-ci.yml` file is [configured properly for pipelines for merge requests](../index.md#configuring-pipelines-for-merge-requests),
-otherwise pipelines for merged results won't run and your merge requests will be stuck in an unresolved state.
+Generally, this is a safer option than merging merge requests immediately, because your
+merge request will be evaluated with an expected post-merge result before the actual
+merge happens.
+
+For more information, read the [documentation on Merge Trains](merge_trains/index.md).
 
 ## Automatic pipeline cancelation
 
@@ -118,15 +128,3 @@ which indicates that the checkout-SHA is not found in the merge ref.
 
 This behavior was improved at GitLab 12.4 by introducing [Persistent pipeline refs](../../pipelines/index.md#troubleshooting-fatal-reference-is-not-a-tree).
 You should be able to create pipelines at any timings without concerning the error.
-
-## Using Merge Trains **(PREMIUM)**
-
-By enabling [Pipelines for merged results](#pipelines-for-merged-results-premium),
-GitLab will [automatically display](merge_trains/index.md#how-to-add-a-merge-request-to-a-merge-train)
-a **Start/Add Merge Train button** as the most recommended merge strategy.
-
-Generally, this is a safer option than merging merge requests immediately as your
-merge request will be evaluated with an expected post-merge result before the actual
-merge happens.
-
-For more information, read the [documentation on Merge Trains](merge_trains/index.md).