Please read the notes in the parent folder.
The RTClib.cpp and RTClib.h files can be placed into your Arduino sketchbooks's library/ folder for use in other projects as well.
Please download Carlos Rodrigues' Barebones ATmega Chips board configuration file: https://github.com/carlosefr/atmega (instructions inside)
The boards.txt file is not needed for newer Arduino IDE versions that include the Boards Manager (under Tools -> Board).
For old versions of the Arduino IDE, it should be placed into a subfolder inside the hardware/ folder of your Arduino sketchbook. E.g. hardware/barebones/boards.txt.
RTClib code by JeeLabs released to the public domain.