Adding the repository is as simple as running the following command from your Raspberry Pi.
curl -sLS https://apt.adafruit.com/add | sudo bash
If you would like to see what the script is doing, you can open it in a web browser before running it.
Warning: apt.adafruit.com contains a new kernel for the PiTFT, and currently the PiTFT kernel will install if you run an apt-get upgrade. This should not be a problem unless you have a custom kernel installed. We are working on resolving this issue, and you can monitor this GitHub issue for updates.
Manually Adding the Repository
If you would like to manually add the repository to your Raspberry Pi, you can start by adding the apt.adafruit.com repository URL to your /etc/apt/sources.list.
echo "deb http://apt.adafruit.com/raspbian/ jessie main" | sudo tee --append /etc/apt/sources.list
Next, you can add the GPG key for apt.adafruit.com.
wget -O - -q https://apt.adafruit.com/apt.adafruit.com.gpg.key | sudo apt-key add -
Finally, you need to download the new package lists from the repos.
sudo apt-get update
