Tags need to be created by someone - usually after a question is created.
I guess the smart thing to do is to ask a question, making it unambiguous to what i2p is. Make sure folks with enough reputation know (but you have!). Include other, appropriate tags and once the i2p tag is created, help fill in the tag wiki - try not to copy sources but paraphrase and refine to fit our needs better.
Folks will help, just get the ball rolling.