Just create it yourself. Use Create a wiki link, the settings there:
Subdomain - gravitac (this is what appears in URL, i.e. gravitac.shoutwiki.com)
Site name - GraviTac
Language of the wiki - zh-cn I guess
Check Include language prefix in URL (this will add the language code to URL, i.e. zh.gravitac.shoutwiki.com)
Your wiki type - I set public, but you can choose another
Category - Gaming
Description - look here: http://www.shoutwiki.com/wiki/GraviTac, this is what I wrote for my wikis. Essentially the description is just for that page. But keep in mind, you can't change it after you create the wiki, you need to contact support for that.
Oh, this one is weird. I had the same troubles before. You need to confirm your e-mail from the main ShoutWiki page, not from any other wiki, as far as I remember.
Dane is a good choice I think for contributing..I'm not sure I can explain things well enough with regards to the game and making it easy to understand for newbies..
Well, wiki is not just for newbies. You can write just what you want (Graviteam Tactics related of course), if something is wrong, me or someone else will sort it out.