Added the API definition for `_suggest`

rest-api-spec/api/suggest.json

@@ -7,24 +7,36 @@
       "paths": ["/_suggest", "/{index}/_suggest"],
       "parts": {
         "index": {
+          "type" : "list",
+          "description" : "A comma-separated list of index names to restrict the operation; use `_all` or empty string to perform the operation on all indices"
         }
       },
       "params": {
         "ignore_indices": {
-        },
-        "index": {
+          "type" : "enum",
+          "options" : ["none","missing"],
+          "default" : "none",
+          "description" : "When performed on multiple indices, allows to ignore `missing` ones"
         },
         "operation_threading": {
+          "description" : "TODO: ?"
         },
         "preference": {
+          "type" : "string",
+          "description" : "Specify the shards the operation should be performed on (default: random shard)"
         },
         "routing": {
+          "type" : "string",
+          "description" : "Specific routing value"
         },
         "source": {
+          "type" : "string",
+          "description" : "The URL-encoded request definition (instead of using request body)"
         }
       }
     },
     "body": {
+      "description" : "The request definition"
     }
   }
 }