You'll need to install the Adafruit_Blinka library that provides the CircuitPython support in Python. This may also require enabling SPI on your platform and verifying you are running Python 3. Since each platform is a little different, and Linux changes often, please visit the CircuitPython on Linux guide to get your computer ready!
Once that's done, from your command line run the following command:
pip3 install adafruit-circuitpython-pcd8544
If your default Python is version 3 you may need to run 'pip' instead. Just make sure you aren't trying to use CircuitPython on Python 2.x, it isn't supported!
If that complains about pip3 not being installed, then run this first to install it:
sudo apt-get install python3-pip
Raspberry Pi usually comes with the DejaVu font already installed, but in case it didn't, you can run the following to install it:
sudo apt-get install ttf-dejavu
We also need PIL, the Python Imaging Library, to allow using text with custom fonts. There are several system libraries that PIL relies on, so installing via a package manager is the easiest way to bring in everything:
sudo apt-get install python3-pil
That's it. You should be ready to go.