docs: add a simple chat client for example (#119)

1. optimize the readme in root
2. add example

Signed-off-by: jokemanfire <hu.dingyang@zte.com.cn>

examples/simple-chat-client/src/lib.rs

@@ -0,0 +1,6 @@
+pub mod chat;
+pub mod client;
+pub mod config;
+pub mod error;
+pub mod model;
+pub mod tool;