message: Fix docs: Bindeps env vars are passed to build script at runtime
  The environment variables are not available through the `env!` macro. Instead, they are passed by cargo when the build script is invoked.
diff: @@ -886,7 +886,7 @@ bar = { artifact = "cdylib", version = "1.0", target = "wasm32-unknown-unknown"
  ```rust
  fn main() {
  - wasm::run_file(env!("CARGO_CDYLIB_FILE_BAR"));
  + wasm::run_file(std::env::var("CARGO_CDYLIB_FILE_BAR").unwrap());
  }
  ```
  