update WithDecoder comment

config/options.go

@@ -33,6 +33,10 @@ func WithSource(s ...Source) Option {
 }
 
 // WithDecoder with config decoder.
+// DefaultDecoder behavior:
+// If KeyValue.Format is non-empty, then KeyValue.Value will be deserialized into map[string]interface{}
+// and stored in the config cache(map[string]interface{})
+// if KeyValue.Format is empty,{KeyValue.Key : KeyValue.Value} will be stored in config cache(map[string]interface{})
 func WithDecoder(d Decoder) Option {
 	return func(o *options) {
 		o.decoder = d