message: fix(doc): update readme code example
diff: @@ -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 extern fn greet(name: &str) {
  + pub fn greet(name: &str) {
  alert(&format!("Hello, {}!", name));
  }
  ```
  