Refined documentation as per...

Refined documentation as per https://gitlab.com/gitlab-org/gitlab/-/merge_requests/32382#note_344100963

doc/api/pipelines.md

 # Pipelines API
 
+## Pipelines pagination
+
+By default, `GET` requests return 20 results at a time because the API results
+are paginated.
+
+Read more on [pagination](README.md#pagination).
+
 ## List project pipelines
 
 > [Introduced](https://gitlab.com/gitlab-org/gitlab-foss/-/merge_requests/5837) in GitLab 8.11