Legacy

This information is dated and may not be the correct method, some distros have these packaged appropriately in pacman/apt-get.

Setup

After installing Archlinux you'll need to setup a few things, namely Python and pip which will help us most of the way.

sudo pacman -S python-pip i2c-tools python 
sudo pip install sense-hat

Next we need a missing python module that's not in AUR

git clone https://github.com/RPi-Distro/RTIMULib.git
cd RTIMULib/Linux/python/
sudo python setup.py build
sudo python setup.py install

And finally we need to enable the modules on boot by modifying

append:

dtparam=i2c_arm=on

append:

i2c-dev
i2c-bcm2708