add statuses to nixpkgs

README.md

@@ -1,6 +1,8 @@
 Nixpkgs is a collection of packages for [Nix](https://nixos.org/nix/) package
 manager.
 
+[![Build Status](https://travis-ci.org/NixOS/nixpkgs.svg?branch=master)](https://travis-ci.org/NixOS/nixpkgs) [![Issue Stats](http://www.issuestats.com/github/nixos/nixpkgs/badge/pr)](http://www.issuestats.com/github/nixos/nixpkgs) [![Issue Stats](http://www.issuestats.com/github/nixos/nixpkgs/badge/issue)](http://www.issuestats.com/github/nixos/nixpkgs)
+
 [NixOS](https://nixos.org/nixos/) linux distribution source code is located inside `nixos/` folder.
 
 * [NixOS installation instructions](https://nixos.org/nixos/manual/#ch-installation)