Added the API definition for `_settings`

rest-api-spec/api/indices.settings.json

@@ -1,19 +1,22 @@
 {
   "indices.settings": {
-    "documentation": "http://elasticsearch.org/guide/reference/api/admin-indices-delete-index/",
+    "documentation": "http://www.elasticsearch.org/guide/reference/api/admin-indices-get-settings/",
     "methods": ["GET", "PUT"],
     "url": {
       "path": "/_settings",
       "paths": ["/_settings", "/{index}/_settings"],
       "parts": {
         "index": {
+          "type" : "list",
+          "required" : true,
+          "description" : "A comma-separated list of index names; use `_all` or empty string to perform the operation on all indices"
         }
       },
       "params": {
-        "index": {
-        }
       }
     },
-    "body": null
+    "body": {
+      "description" : "The index settings to be updated (when using the PUT method)"
+    }
   }
 }