This was a fun easy introduction to using Particle.io. Building/installing the code is done easily through the Particle cloud. See the README.md in my source code.
The electrical assembly was also easy - See the photo for how I soldered the sensor board onto D1/D0 and attached jumpers to 3.3V and ground. I'd recommend flipping the board over so that it sticks out away from the Photon because in its current position it gets heated some by the Photon (which is not ideal).
I installed webhooks on the Particle.io console to send the published data to adafruit.io. Send me a note if you'd like me to add details on that step. My live console on Adafruit.io is here.
If the board detects a humidity reading that is too high it will publish an 'alarm-humidity' event. You can use that event in IFTTT to notify you that there is a problem.