Change format badge from BBF1 to BBF3

Updated badge to reflect BBF3 format version.

Author: ef1500

readme.md

@@ -1,6 +1,6 @@
 # libbbf: Bound Book Format 
 
-![alt text](https://img.shields.io/badge/Format-BBF1-blue.svg)
+![alt text](https://img.shields.io/badge/Format-BBF3-blue.svg)
 ![alt text](https://img.shields.io/badge/License-MIT-green.svg)
 
 > [!WARNING]