Install WebIOPi onto the Raspberry Pi https://code.google.com/p/webiopi/wiki/INSTALL?tm=6
Next create a custom HTML page and a python file to help it. This will allow us to use one large button instead of many small ones. You can view the code in this project here: https://github.com/electrodog10/Model-Rocket-Launc...
You can see how to change the default WebIOPi page here:
Also connect the Pi to the Wifi hotspot you will use when flying the rocket. Check out a tutorial for that here: https://learn.adafruit.com/adafruits-raspberry-pi-lesson-3-network-setup/setting-up-wifi-with-occidentalis
Connect the power, signal, and ground wires between the Raspberry Pi and relay board. Connect the relay board output to act as a switch on the +9V coming off of the 9 volt battery. Once that is done, connect the 9V battery to the rocket igniter.
Finally power up the Pi and your wifi source and you are ready to reach new heights!!