If u already have an Adafruit rgb lcd Pi Plate for the Raspberry Pi u can use it also to your project with an Arduino.
First we have to find the pins that we have to use in order to make the lcd usable. We need the pins 5V, GND, SDA and SCL.
As you can see in the picture we have 4 wires A,B,C,D.
WIre A (pin 3) goes to SDA.
WIre B (pin 5) goes to SCL.
Wire C (pin 2) goes to 5V.
Wire D (pin 6) goes to GND.
If u have an Arduino UNo rev.3 u can use also analog pin A4 for SDA and analog pin A5 for SCL.
Now in order to use the lcd you must download 2 libraries.
First OneWire from here Arduino Playground - OneWire and also Adafruit library from here.https://learn.adafruit.com/rgb-lcd-shield/using-the-rgb-lcd-shield
A small demo video where u can see that the lcd is working fine.