Update Readme file to contain AppVeyor badge

Update Readme file to contain AppVeyor build status

README.md

@@ -1,4 +1,4 @@
-# Source Map Toolkit
+# Source Map Toolkit [![Build status](https://ci.appveyor.com/api/projects/status/8ydsci6e4v80n6c0?svg=true)](https://ci.appveyor.com/project/thomabr/sourcemap-toolkit)
 This is a C# library for working with JavaScript source maps and deminifying JavaScript callstacks.
 
 ## Source Map Parsing
@@ -133,4 +133,4 @@ The unit tests for this library leverage the functionality provided by [Rhino Mo
 ## License
 Copyright (c) Microsoft Corporation. All rights reserved.
 
-Licensed under the [MIT](LICENSE.txt) License.
+Licensed under the [MIT](LICENSE.txt) License.