message: Update src/lib.rs
diff: //! img2.write_to(&mut bytes, image::ImageOutputFormat::Png)?;
  //! # Ok(())
  //! # }
  +//! # #[cfg(not(feature = "png"))] fn main() {}
  //! ```
  //!
  //! With default features, the crate includes support for [many common image formats](codecs/index.html#supported-formats).
  