I think it's completely appropriate to include only yourselves as the parents if you wish. If you'd like to acknowledge the birthparents, that's nice too, but as a bmom, I wouldn't be hurt if I wasn't on the announcement.
I've seen lots of adoption announcements worded something like:
We're pleased to announce the arrival (adoption) of "Baby Doe"
Born Oct 31, 2006 at 7:30 PM
In our arms forever on November 5, 2006 (if you wish to include the date baby came home)
7 pounds, 3 ounces
19 inches
Proud parents John and Jane Doe
If you Google "adoption announcements" you can find tons of websites offering baby announcements with a lot of sample wording that you may like better.
Best of luck with your match.
