Update README.md

Author: ehsan6sha

README.md

@@ -26,6 +26,7 @@ await fula.init(
  identity: string, //bytes of the privateKey of did identity in string format
  storePath: string, // leave empty to use the default temp one
  bloxAddr: string, //leave empty for testing without a backend node
+ exchange: 'noop'|'' //add noop for testing without a backend
 );
 ```