Added the API definition for opening an index

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

@@ -1,18 +1,20 @@
 {
   "indices.open": {
-    "documentation": "",
+    "documentation": "http://www.elasticsearch.org/guide/reference/api/admin-indices-open-close/",
     "methods": ["POST"],
     "url": {
       "path": "/{index}/_open",
       "paths": ["/{index}/_open"],
       "parts": {
         "index": {
+          "type" : "string",
+          "description" : "The name of the index to close"
         }
       },
       "params": {
-        "index": {
-        },
         "timeout": {
+          "type" : "time",
+          "description" : "Explicit operation timeout"
         }
       }
     },