To read this sensor on the Pi, you can use one of two methods.
First of all, you could have Arduino read the sensor and send the readings back to the Raspberry Pi, over a connection, either I2C, Serial or USB. For an example of the USB method, check out Simon Monk's blog at: http://www.doctormonk.com/2012/04/raspberry-pi-and-arduino.html
Be aware that if you use a pin-to-pin connection, you might need a level converter in there somewhere to make sure that the Arduino's 5V is not transmitted to the Pi's 3v3 pin logic.
Alternatively, you could connect up an analog to digital converter and communicate with the chip over SPI. There are a number of blog posts out there, but the first one to look at is over at Raspberry Pi Spy - http://www.raspberrypi-spy.co.uk/2013/10/analogue-sensors-on-the-raspberry-pi-using-an-mcp3008/
This will give you a clear example of how to wire up the chip.
If you don't want to wire up the chip yourself, I recommend the RasPiO Analog Zero board which has just gone on pre-order (and will be available very soon otherwise I wouldn't have mentioned it!) at http://rasp.io/analogzero
You might need a voltage divider to take the 5V output of the gas sensor down to 3V3. However, in my experience of using multiple gas sensors with the same analog-to-digital chip, you can just put the 5V of the gas sensor into the MCP3008 and the Pi will be fine.
If you are going to use an analog-to-digital converter, take a look at Alex Eames' blog post here: http://raspi.tv/2016/using-mcp3008-to-measure-temperature-with-gpio-zero-and-raspio-pro-hat
He takes you through using the GPIO Zero library (http://gpiozero.readthedocs.io) to read an analog sensor through an MCP3008.