[placement] add api-ref for GET /resource_providers

This provides simple documentation of the response body and query
parameters when listing resource providers.

Change-Id: Ic8db81b5f17d4c380b64b3da24e525297db18584

placement-api-ref/source/index.rst

@@ -44,3 +44,52 @@ Response Example
 
 .. literalinclude:: get-root.json
    :language: javascript
+
+==================
+Resource Providers
+==================
+
+Resource providers are entities which provide consumable inventory of one or
+more classes of resource (such as disk or memory). They can be listed (with
+filters), created, updated and deleted.
+
+List Resource Providers
+=======================
+
+.. rest_method:: GET /resource_providers
+
+List an optionally filtered collection of resource providers.
+
+Normal Response Codes: 200
+
+Request
+-------
+
+Several query parameters are available to filter the returned list of
+resource providers. If multiple different parameters are provided, the results
+of all filters are merged with a boolean `AND`.
+
+.. rest_parameters:: parameters.yaml
+
+  - resources: resources_query
+  - member_of: member_of
+  - uuid: resource_provider_uuid_query
+  - name: resource_provider_name_query
+
+Response
+--------
+
+.. rest_parameters:: parameters.yaml
+
+  - resource_providers: resource_providers
+  - generation: resource_provider_generation
+  - uuid: resource_provider_uuid
+  - links: resource_provider_links
+  - name: resource_provider_name
+
+
+Response Example
+----------------
+
+.. literalinclude:: get-resource_providers.json
+   :language: javascript