add Sauce Labs credits

Author: gfx

README.md

@@ -1,6 +1,6 @@
 # MessagePack for JavaScript [![npm version](https://badge.fury.io/js/%40msgpack%2Fmsgpack.svg)](https://badge.fury.io/js/%40msgpack%2Fmsgpack) [![Build Status](https://travis-ci.org/msgpack/msgpack-javascript.svg?branch=master)](https://travis-ci.org/msgpack/msgpack-javascript) [![codecov](https://codecov.io/gh/msgpack/msgpack-javascript/branch/master/graph/badge.svg)](https://codecov.io/gh/msgpack/msgpack-javascript)
 
-[![Browser Matrix](https://saucelabs.com/browser-matrix/gfx2019.svg)](https://saucelabs.com)
+[![Browser Matrix powered by Sauce Labs](https://saucelabs.com/browser-matrix/gfx2019.svg)](https://saucelabs.com)
 
 This is a JavaScript/ECMA-262 implementation of **MessagePack**, an efficient binary serilization format:
 
@@ -219,6 +219,12 @@ git push origin master
 make publish
 ```
 
+### Big Thanks
+
+Cross-browser Testing Platform and Open Source <3 Provided by Sauce Labs.
+
+[![Sauce Labs](./assets/SauceLabs.svg)](https://saucelabs.com)
+
 ## License
 
 Copyright 2019 The MessagePack community.