The project uses three code libraries:
- Wire.h - the Arduino standard library for I2C/two wire communication (already installed with the Arduino IDE)
- RTClib - Used to communicate with the DS1307 real-time clock
- Adafruit_RGBLCDShield - communicates with the Adafruit RGB LCD Shield
You may click on the links to download from the Adafruit Github repository.
These should be installed in your Arduino folder where your sketches are stored in the libraries folder. For an in-depth discussion of installing and managing Arduino libraries, see tutorial All About Arduino Libraries.
If you use the Arduino IDE version 1.6.5 or later, you can download the Adafruit board file in the Tools -> Board -> Board Manager. You will then be able to select "Trinket 8 MHz" as a board and all is well.