Added TravisCI build status in README.md file

Signed-off-by: Cydh Ramdh <house.bad@gmail.com>

README.md

@@ -1,5 +1,8 @@
 rAthena
 =======
+
+Build Status: [![Build Status](https://travis-ci.org/rathena/rathena.png?branch=master)](https://travis-ci.org/rathena/rathena)
+
 Table of Contents
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 * 1 What is rAthena?