[DOCS] Formatted the privileges API (elastic/x-pack-elasticsearch#2575)

Original commit: elastic/x-pack-elasticsearch@9080eb9535

docs/en/rest-api/security/privileges.asciidoc

@@ -7,13 +7,41 @@
 The `has_privileges` API allows you to determine whether the logged in user has
 a specified list of privileges.
 
+==== Request
+
+`GET _xpack/security/user/_has_privileges`
+
+
+==== Description
+
+For a list of the privileges that you can specify in this API,
+see {xpack-ref}/security-privileges.html[Security Privileges].
+
+A successful call returns a JSON structure that shows whether each specified
+privilege is assigned to the user.
+
+
+==== Request Body
+
+`cluster`:: (list) A list of the cluster privileges that you want to check.
+
+`index`::
+`names`::: (list) A list of indices.
+`privileges`::: (list) A list of the privileges that you want to check for the
+specified indices.
+
+==== Authorization
+
 All users can use this API, but only to determine their own privileges.
 To check the privileges of other users, you must use the run as feature. For
 more information, see
 {xpack-ref}/run-as-privilege.html[Submitting Requests on Behalf of Other Users].
 
-To check you privileges, submit a GET request to the
-`_xpack/security/user/_has_privileges` endpoint:
+
+==== Examples
+
+The following example checks whether the current user has a specific set of
+cluster and indices privileges:
 
 [source,js]
 --------------------------------------------------
@@ -34,8 +62,7 @@ GET _xpack/security/user/_has_privileges
 --------------------------------------------------
 // CONSOLE
 
-A successful call returns a JSON structure that shows whether each specified
-privilege is assigned to the user
+The following example output indicates which privileges the "rdeniro" user has:
 
 [source,js]
 --------------------------------------------------