The text mentions two ways a Sadguru receives service through books. What are they, and can you give examples?

Chapter 0 outlines the two primary methods through which a Sadguru accepts service from devotees via books. The first method is when the Guru creates great spiritual works themselves, with cited examples being Shri Dnyaneshwari and Shri Dasbodh. The second method is when the Guru has their biographies written by devotees. The service is then rendered through the study and devotional readings (Parayans) of these biographies by both the writer and the larger community of devotees. A prime example of this second type is the Shri Sai Satcharita, written by Annasaheb Dabholkar about Sai Baba.