"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/jobs."
humanstxt.org/ The official website :-)
It has been twitted by @googlejobs yesterday ;-)
JEShack: It' recommended to add the source on this forum.
Juha: I've just discovered it using chrome extension.
Tim from Google announced it on Saturday