Merge pull request #36 from rogerz/auto-ci

Add building status image in README

README.md

@@ -1,4 +1,6 @@
 RT-Thread
 =========
 
+[![Build Status](https://travis-ci.org/RT-Thread/rt-thread.png)](https://travis-ci.org/RT-Thread/rt-thread)
+
 RT-Thread is an open source real-time operating system for embedded devices.