You should realize one thing though: not everyone uses Facebook, although it's VERY widely used you might be counterproductive by sourcing it to a members only source.
You can go to your profile and add websites to your profile under edit profile. There you can grab your Facebook fan page/ group page url and click and past it into your links section. As a PRO on here you should have the greatest opportunites to linking & features. You should read up on non-follow tags & their use on sites like this though.
Hope that helps,