Update pipelines api docs

doc/api/jobs.md

@@ -294,7 +294,7 @@ Example of response
 ]
 ```
 
-In GitLab 13.3 and later, this endpoint [returns data for any pipeline](pipelines.md#single-pipeline-requests)
+In GitLab 13.3 and later, this endpoint [returns data for any pipeline](pipelines.md#get-a-single-pipeline)
 including [child pipelines](../ci/pipelines/parent_child_pipelines.md).
 
 In GitLab 13.5 and later, this endpoint does not return retried jobs in the response

doc/api/pipelines.md

@@ -6,14 +6,6 @@ info: To determine the technical writer assigned to the Stage/Group associated w
 
 # Pipelines API **(FREE)**
 
-## Single Pipeline Requests
-
-> [Introduced](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/36494) in GitLab 13.3.
-
-Endpoints that request information about a single pipeline return data for any pipeline.
-Before 13.3, requests for [child pipelines](../ci/pipelines/parent_child_pipelines.md) returned
-a 404 error.
-
 ## Pipelines pagination
 
 By default, `GET` requests return 20 results at a time because the API results
@@ -23,6 +15,9 @@ Read more on [pagination](index.md#pagination).
 
 ## List project pipelines
 
+List pipelines in a project. Child pipelines are not included in the results,
+but you can [get child pipeline](pipelines.md#get-a-single-pipeline) individually.
+
 ```plaintext
 GET /projects/:id/pipelines
 ```
@@ -79,6 +74,11 @@ Example of response
 
 ## Get a single pipeline
 
+Get one pipeline from a project.
+
+You can also get a single [child pipeline](../ci/pipelines/parent_child_pipelines.md).
+[Introduced](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/36494) in GitLab 13.3.
+
 ```plaintext
 GET /projects/:id/pipelines/:pipeline_id
 ```

doc/user/analytics/ci_cd_analytics.md

@@ -21,6 +21,12 @@ View pipeline duration history:
 
 ![Pipeline duration](img/pipelines_duration_chart.png)
 
+Pipeline statistics are gathered by collecting all available pipelines for the
+project regardless of status. The data available for each individual day is based
+on when the pipeline was created. The total pipeline calculation includes child
+pipelines and pipelines that failed with invalid YAML. If you are interested in
+filtering pipelines based on other attributes, consider using the [Pipelines API](../../api/pipelines.md#list-project-pipelines).
+
 ## DevOps Research and Assessment (DORA) key metrics **(ULTIMATE)**
 
 > - [Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/275991) in GitLab 13.7.