Hi Dave,
To get DHT22 to work, you just need the DHT22 library:
https://github.com/adafruit/DHT-sensor-library
and it requires a spare GPIO pin. On OpenGarage, GPIO 4 and 5 are spare pins and are mapped out, so you can use either of them.
Alternatively, there are I2C versions of DHT22 (for example, AM2320). GPIO 4 and 5 happen to be the hardware I2C SDA and SCL pins respectively, so you can also use AM2320. The library for AM2320 can be found here:
https://github.com/thakshak/AM2320