Added build status badges to README.md.

README.md

@@ -1,6 +1,9 @@
 cmark
 =====
 
+[![Build Status]](https://travis-ci.org/jgm/cmark)
+[![Windows Build Status]](https://ci.appveyor.com/project/jgm/cmark)
+
 `cmark` is the C reference implementation of [CommonMark], a
 rationalized version of Markdown syntax with a [spec][the spec].
 (For the JavaScript reference implementation, see
@@ -158,3 +161,5 @@ most of the C library's API and its test harness.
 [cmake]: http://www.cmake.org/download/
 [re2c]: http://re2c.org
 [commonmark.js]: https://github.com/jgm/commonmark.js
+[Build Status]: https://img.shields.io/travis/jgm/cmark/master.svg?style=flat
+[Windows Build Status]: https://ci.appveyor.com/api/projects/status/32r7s2skrgm9ubva?svg=true