Merge branch 'custom-role-ui-bill' into 'master'

Add note on overcharge

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/138935



Merged-by: Fiona Neill <fneill@gitlab.com>
Approved-by: Eduardo Sanz García <esanz-garcia@gitlab.com>
Approved-by: Fiona Neill <fneill@gitlab.com>
Co-authored-by: Jonathan Glassman <jglassman@gitlab.com>

doc/user/custom_roles.md

@@ -153,6 +153,9 @@ To add a user to your group with a custom role:
 
 The new member with custom role and custom permissions appears on the [group's members list](group/index.md#view-group-members).
 
+NOTE:
+Most custom roles are considered [billable users that use a seat](#billing-and-seat-usage). When you add a user to your group with a custom role, a warning is displayed if you are about to incur additional charges for having more seats than are included in your subscription.
+
 ### Change a member's custom role
 
 To change a group member's custom role: