Add documentation for API 'validate_setup_for_nested_quota_use'

Documentation for API 'validate_setup_for_nested_quota_use' is
missing. Fix it.

Change-Id: Ica3d468856bad045c2bdd30a0f86924cc0aeb572

api-ref/source/v3/parameters.yaml

@@ -220,6 +220,14 @@ detail:
   in: query
   required: false
   type: boolean
+fix_allocated_quotas:
+  description: |
+    Whether to fix all the non-leaf projects' ``allocation``
+    attribute or raise 400 error if ``allocation`` doesn't match
+    the current quota usage information. Default is ``false``.
+  in: query
+  required: false
+  type: boolean
 force_3:
   description: |
     To delete a QoS specification even if it is in-

api-ref/source/v3/quota-sets.inc

@@ -227,3 +227,25 @@ Response Example
 
 .. literalinclude:: ./samples/quotas-show-defaults-response.json
    :language: javascript
+
+
+Validate setup for nested quota
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. rest_method::  GET /v3/{admin_project_id}/os-quota-sets/validate_setup_for_nested_quota_use
+
+Validate setup for nested quota, administrator should ensure that Keystone v3 or greater is
+being used.
+
+
+Normal response codes: 200
+Error response codes: badRequest(400)
+
+
+Request
+-------
+
+.. rest_parameters:: parameters.yaml
+
+   - admin_project_id: admin_project_id
+   - fix_allocated_quotas: fix_allocated_quotas