fix(doc): update readme code example

README.md

@@ -57,7 +57,7 @@ this project is written in rust. [get rust] to work on this project.
     use wasm_bindgen::prelude::*;
   ```
 
-4. annotate your public functions with `#[wasm_bindgen]` and  `#[no_mangle]`, for example:
+4. annotate your public functions with `#[wasm_bindgen]`, for example:
 
   ```rust
   #[wasm_bindgen]
@@ -66,8 +66,7 @@ this project is written in rust. [get rust] to work on this project.
   }
 
   #[wasm_bindgen]
-    #[no_mangle]
+  pub fn greet(name: &str) {
-    pub extern fn greet(name: &str) {
       alert(&format!("Hello, {}!", name));
   }
   ```