Add Travis CI build status.

Change-Id: Ia0ad3b10fc3e2617945fd0ca763f134ef7276fa4
Reviewed-on: https://swiftshader-review.googlesource.com/10088
Reviewed-by: Nicolas Capens <capn@google.com>
Tested-by: Nicolas Capens <capn@google.com>

README.md

diff --git a/README.md b/README.md
index 7088ff3..74a76f3 100644
--- a/README.md
+++ b/README.md
@@ -1,4 +1,4 @@
-SwiftShader

+SwiftShader [![Build Status](https://travis-ci.org/google/swiftshader.svg?branch=master)](https://travis-ci.org/google/swiftshader)

 ==========

 

 Introduction

@@ -84,4 +84,4 @@
 

 1. Trademarks are the property of their respective owners.

 2. We do not claim official conformance with any graphics APIs at this moment.

-3. This is not an official Google product.
\ No newline at end of file
+3. This is not an official Google product.