docs: surface cost attribution a bit more + link to api (#2590)

Author: Pierrci

docs/hub/enterprise-resource-groups.md

@@ -26,6 +26,7 @@ This feature allows organization administrators to:
 - Keep private repositories visible only to authorized group members
 - Enable multiple teams to work independently within the same organization
 - Configure which member roles are allowed to create new resource groups
+- Attribute costs to specific resource groups for better budget management
 
 This Team & Enterprise feature helps organizations manage complex team structures and maintain proper access control over their repositories.
 

docs/hub/security-resource-groups.md

@@ -108,6 +108,8 @@ Resource Groups also serve as a cost attribution unit for compute services. When
 - **Inference Providers**: pass the resource group's ID via the `X-HF-Bill-To` header (or `bill_to` parameter in the SDK). See [Billing for Team and Enterprise organizations](/docs/inference-providers/pricing#billing-for-team-and-enterprise-organizations).
 - **Inference Endpoints**: cost is automatically attributed to the resource group the model repository belongs to. Endpoints instantiated directly from the built-in Inference Endpoints catalog aren't supported at this time.
 
+You can use the <a href="https://huggingface.co/spaces/huggingface/openapi#tag/orgs/GET/api/organizations/&#123;name&#125;/billing/usage-by-resource-group">dedicated API endpoint</a> to retrieve cost attribution data for resource groups.
+
 ## Resource Groups API
 
 You can list resource groups and add users to them (or change a member's org role and resource group assignments) via the Hub API. For the full reference, examples, and batch workflows, see the [Programmatic User Access Control Management](./programmatic-user-access-control) guide.