add build status badge

Author: weltling

Diff for: README.md

@@ -5,6 +5,7 @@ This is the github mirror of the official PHP repository located at
 http://git.php.net.
 
 [![Build Status](https://secure.travis-ci.org/php/php-src.svg?branch=master)](http://travis-ci.org/php/php-src)
+[![Build status](https://ci.appveyor.com/api/projects/status/meyur6fviaxgdwdy?svg=true)](https://ci.appveyor.com/project/php/php-src)
 
 Pull Requests
 =============