Added interval to readme

README.md

@@ -6,7 +6,8 @@ Initiate config fetching. `environment` is one of "dev", "stage" or "prod"
 var configClient = require("next-config-client");
 configClient({
   requestUrl: "ws://example.com/api/vx/config/",
-  environment: "dev"
+  environment: "dev",
+  interval: time in milliseconds
 })
 .then((config) => {
   // Do stuff with config and start app