Add API documentation for volume detach in v3.

Change-Id: Id8211478bf093b28ea568f741c6e8b34f3696e0c
Closes-Bug: #1671372

api-ref/source/v3/parameters.yaml

@@ -1206,6 +1206,12 @@ os-attach:
   in: body
   required: true
   type: object
+os-detach:
+  description: |
+    The ``os-detach`` action.
+  in: body
+  required: true
+  type: object
 os-extend:
   description: |
     The ``os-extend`` action.

api-ref/source/v3/samples/volume-detach-request.json

@@ -0,0 +1,6 @@
+{
+    "os-detach": {
+        "attachment_id": "d8777f54-84cf-4809-a679-468ffed56cf1"
+    }
+}
+

api-ref/source/v3/volumes-v3-volumes-actions.inc

@@ -195,6 +195,42 @@ Request Example
 
 
 
+Detach volume from server
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. rest_method::  POST /v3/{project_id}/volumes/{volume_id}/action
+
+Detaches a volume from a server. Specify the ``os-detach`` action in the request body.
+
+Preconditions
+
+- Volume status must be ``in-use``.
+
+Normal response codes: 202
+
+
+Request
+-------
+
+.. rest_parameters:: parameters.yaml
+
+   - attachment_id: attachment_id
+   - os-detach: os-detach
+   - project_id: project_id_path
+   - volume_id: volume_id
+
+Request Example
+---------------
+
+.. literalinclude:: ./samples/volume-detach-request.json
+   :language: javascript
+
+
+
+
+
+
+
 Unmanage a volume
 ~~~~~~~~~~~~~~~~~