The adafruit_io_feed.ino was taken from https://github.com/adafruit/Adafruit_IO_Arduino/tree/master/examples/adafruitio_21_feed_read and adjusted a little bit. The example was for a shared file. This example only reads via MQTT, so data must change to see it. You will need the config.h file with your key and wifi set up.
I needed to install the Adafruit Mqtt and the Arduino HTTP client as dependencies with the Adafruit IO library.
This was pieced together from examples I found. It uses the Arduino Http client to make an http request to get a feed from Adafruit IO. You will need to enter your Wifi and IAO credentials at the top.