must use & instead of ? -- needs clarification

I was excited to find this module but have had some trouble implementing it. For one thing, the README.txt file is still (again?) empty, and if there is a help screen, I can't find it anywhere. So I read through the issues here and found that I'm supposed to be able to use links of the format
example.com/contact?category=foo
But instead I found (by trial and error) that they only work in the format
example.com/contact&category=foo

I can live with that, but it's not at all clear from what little documentation is here. Please help out your fellow Webmasters and document this module! Thanks!