Merge branch 'docs/adding-group-api-link' into 'master'

Docs: Adding link to group milestones api for clarification

See merge request gitlab-org/gitlab!33323

doc/api/milestones.md

@@ -6,6 +6,9 @@ info: To determine the technical writer assigned to the Stage/Group associated w
 
 # Project milestones API
 
+This page describes the project milestones API.
+There's a separate [group milestones API](./group_milestones.md) page.
+
 ## List project milestones
 
 Returns a list of project milestones.