Mentioning NGINX and added info about groups for tests | Related to #144

A small update to the doc to make it more general. As discussed with @dbu I'm going to send small PR for each update to avoid thing to diverge to much.

This is the first one.
Heh. :smile: By the way, both the Nginx website and Wikipedia spell ‘nginx’ (without any capitals), which looks silly to me but could be considered the official spelling.