Update README.md

Author: bboyho

README.md

@@ -23,7 +23,8 @@ Documentation
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 * **[Installing an Arduino Library Guide](https://learn.sparkfun.com/tutorials/installing-an-arduino-library)** - Basic information on how to install an Arduino library.
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+* **[Hookup Guide](https://docs.sparkfun.com/SparkFun_Serial_MP3_Player_Shield-MY1690X/)** - Tutorial for the SparkFun Serial MP3 Player Shield - MY1690X
+* **[GitHub Hardware Repo](https://github.com/sparkfun/SparkFun_Serial_MP3_Player_Shield-MY1690X)** - Hardware design files and documentation.
 
 Products that use this Library 
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