Please note that there is no "SIT User Group" per se. Rather, there is a Portfolio Plus User Group and you can find out all the information on how to join it on this Portfolio Plus User Group page. This group is only open to customers of SIT.
If you're not a customer and would simply like to follow SIT's marketing announcements (and other activities) you may be interested in joining the Portfolio Plus Group on LinkedIn. This group is open to anybody who wants to join.