Add two books to the golang section of getting started

Signed-off-by: Richard Gee <[email protected]>

Author: rgee0

docs/contributing/get-started.md

@@ -31,6 +31,8 @@ If you are new with Docker, Kubernetes or Go and would like to learn or just imp
     * [The Case For Go](https://gist.github.com/ungerik/3731476) - a list of sources collected by Erik Unger
     * Another interesting blog post - [Why should you learn Go?](https://medium.com/@kevalpatel2106/why-should-you-learn-go-f607681fad65) by Keval Patel
     * Official Golang [GitHUb](https://github.com/golang) account
+    * [The Go Programming Language (Addison-Wesley Professional Computing)](https://www.amazon.co.uk/Programming-Language-Addison-Wesley-Professional-Computing/dp/0134190440)
+    * [The Clean Coder: A Code of Conduct for Professional Programmers (Robert C. Martin)](https://www.amazon.co.uk/Clean-Coder-Conduct-Professional-Programmers/dp/0137081073/ref=sr_1_1?s=books&ie=UTF8&qid=1543083898&sr=1-1&keywords=the+clean+coder)
 * [Travis CI User Documentation](https://docs.travis-ci.com)
 
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