I've never heard of this. I wonder how many websites implement this. I tried a bunch of sites, but the only one I could find that had a humans.txt file was google:
Google is built by a large team of engineers, designers, researchers, robots, and others in many different sites across the globe. It is updated continuously, and built with more tools and technologies than we can shake a stick at. If you'd like to help us out, see google.com/careers.