(Not to be confused with Lifeline Universe)
From Wikipedia (Section 5):
"Lifeline Library [Released around Jan. 2017, according to App Shopper] is a mobile app designed to give users "exclusive first access to news, updates, and new stories." Users have access to artwork relating to the game, and access to Lifeline: Silent Night, Lifeline: Whiteout, and the first chapter of Lifeline: Whiteout 2."
All credit goes to the people editing the Lifeline page on Wikipedia!
Note: Lifeline Library app is discontinued, not sure of the exact shutdown, app last updated 06-30-2017 according to App Shopper , can't find on Google Play or App Store