Add gitter link to README

Author: Susurrus

README.md

@@ -81,6 +81,9 @@ extern crate nix;
 Contributions are very welcome.  Please See [CONTRIBUTING](CONTRIBUTING.md) for
 additional details.
 
+Feel free to join us in [the nix-rust/nix](https://gitter.im/nix-rust/nix) channel on Gitter to
+discuss `nix` development.
+
 ## License
 
 Nix is licensed under the MIT license.  See [LICENSE](LICENSE) for more details.