mention go and rust toolchains (#1264)

Author: dcharkes

README.md

@@ -19,6 +19,15 @@ building and bundling.
 | [native_assets_cli](pkgs/native_assets_cli/) | A library that contains the argument and file formats for implementing a native assets CLI. | [![pub package](https://img.shields.io/pub/v/native_assets_cli.svg)](https://pub.dev/packages/native_assets_cli) |
 | [native_toolchain_c](pkgs/native_toolchain_c/) | A library to invoke the native C compiler installed on the host machine. | [![pub package](https://img.shields.io/pub/v/native_toolchain_c.svg)](https://pub.dev/packages/native_toolchain_c) |
 
+## External packages
+
+Packages not on this repo but also related to FFI and native assets. ❤️
+
+| Package | Description | Version |
+| --- | --- | --- |
+| [native_toolchain_go](https://github.com/csnewman/flutter-go-bridge/tree/master/native_toolchain_go) | A library to invoke the native Go compiler installed on the host machine. | [![pub package](https://img.shields.io/pub/v/native_toolchain_go.svg)](https://pub.dev/packages/native_toolchain_go) |
+| [native_toolchain_rust](https://github.com/irondash/native_toolchain_rust) | A library to invoke the native Rust compiler installed on the host machine. | [![pub package](https://img.shields.io/pub/v/native_toolchain_rust.svg)](https://pub.dev/packages/native_toolchain_rust) |
+
 ## Publishing automation
 
 For information about our publishing automation and release process, see