According to the preface, what are the two main ways a Sadguru provides literary service to their followers?

The preface explains that a Sadguru offers service to devotees through books in two distinct manners. As outlined in Chapter 0, the first way is by the Sadguru personally authoring great spiritual works, such as the Shri Dnyaneshwari or Shri Dasbodh. The second method involves the Sadguru having their biographies written by their devotees. In this scenario, the Sadguru accepts this act as a form of service, not only from the writer but also from the congregation of devotees who engage in the study and devotional reading (Parayans) of the text.