message: add doc about auth callback
diff: @@ -55,7 +55,7 @@ const app = new Server({
  })
  app.auth(token => {
  - // TODO Return user by token or false on bad token.
  + // TODO Return user by token or false on bad token. It should be Promise.
  })
  app.log.on('event', (event, meta) => {
  