add a code sample

Author: mourner

README

@@ -1,3 +1,11 @@
+## bbtree
 
-A very simple and efficient JavaScript implementation of [Andersson tree](http://user.it.uu.se/~arnea/ps/simp.pdf),
+A very simple JavaScript implementation of [Andersson tree](http://user.it.uu.se/~arnea/ps/simp.pdf),
 a self-balancing binary search tree data structure.
+
+```js
+var tree = bbtree();
+
+tree.insert(1);
+tree.insert(5);
+```