According to the Narada Purana as cited in Chapter 0, what are the specific guidelines for writing a Guru's biography to ensure it is a salvation-granting text?

The provided text in Chapter 0 references the Narada Purana for a very specific and limited purpose. It mentions the Purana only to establish that the service of writing a Guru's biography is a very ancient tradition. However, the source does not cite any specific guidelines or rules from the Narada Purana about how to write such a text to ensure it grants salvation. Instead, Chapter 0 provides its own definition, stating that a Guru's biography is a book describing the Guru's incarnation, life, 'wonderful plays (Leelas),' and miracles, and that studying it selflessly is a form of superior Guru service.