docs: improve onboarding

When getting started with go sdk it's easy to miss waiting for initialization. This change will make it easy for newcomers to use the SDK and more advanced users should be able to wait for the readiness in different ways if they don't want to block the main thread

README.md

@@ -46,6 +46,9 @@ func init() {
 		unleash.WithUrl("http://unleash.herokuapp.com/api/"),
 		unleash.WithCustomHeaders(http.Header{"Authorization": {"<API token>"}}),
 	)
+
+        // The line below will block until the default client is ready or returns immediately. You can wait for readiness in a different way but this is good for new joiners
+        unleash.WaitForReady()
 }
 ```