How do I add a facebook button to Tumblr?

[Bre]

Not a badge, not a like button. just a little button that has my profile link. like this:
http://hannah-christensen.tumblr.com/
I want a button like hers, but just the facebook one. How do I get it?

[Terence]

customize -> pages ->Page URL "/facebook" -> Page Title "facebook" -> and then put your facebook url under where it says " Body" -> then clicked show link to page and clicked create page