Add BAIR's Koala to supported models (#877)

README.md

@@ -42,6 +42,7 @@ New features will probably be added mostly through community contributions.
 - [X] [Chinese LLaMA / Alpaca](https://github.com/ymcui/Chinese-LLaMA-Alpaca)
 - [X] [Vigogne (French)](https://github.com/bofenghuang/vigogne)
 - [X] [Vicuna](https://github.com/ggerganov/llama.cpp/discussions/643#discussioncomment-5533894)
+- [X] [Koala](https://bair.berkeley.edu/blog/2023/04/03/koala/)
 
 **Bindings:**