While documentaries have been an accepted part of filmmaking for a long time, they are more popular than ever now, partly because of the many ways of distribution, as well as the less expensive methods of making them.
Jacob Bricca, who has a long career as a producer, director, and editor, has written a book useful for both the filmmaking student, as well as the fan of documentaries.
Documentary Editing: Principles and Practice (Focal Press, 2018) includes both interesting technical details and breakdowns of a number of famous films.