Add Appveyor badge to Readme.md

Author: BillyDonahue

README.md

@@ -2,6 +2,7 @@
 # Google Test #
 
 [![Build Status](https://travis-ci.org/google/googletest.svg?branch=master)](https://travis-ci.org/google/googletest)
+[![Build status](https://ci.appveyor.com/api/projects/status/4o38plt0xbo1ubc8/branch/master?svg=true)](https://ci.appveyor.com/project/BillyDonahue/googletest/branch/master)
 
 Welcome to **Google Test**, Google's C++ test framework!