I think Mark Summerfield's book is quite a good introduction:

http://www.qtrac.eu/gobook.html

Many of his examples touch upon sysadmin work, such as the MP3 playlist conversion, implementing concurrent grep, and coverage of common file formats (XML, JSON, plain text) and archive formats. It's also a good introduction to Go. At times it drinks the kool-aid a bit to much, it sometimes takes quite mundane constructs as an example how stellar Go is (let's be honest, Go is quite a boring language, but boring can be good at times).

If you understand that they seem to be written as a learning exercises by the respective authors, I found that there's a good introduction to the nuts and bolts to be had browsing attempts at creating userspace tools in go: eg. https://bitbucket.org/telesto/goblin/ or https://github.com/manveru/goblin .. it seems to be a popular first project :)

sysadmin here; I've been enjoying An Introduction to Programming in Go by Caleb Doxsey[1]. Short, sweet, and right to the point without being terse.

There is nothing in this book that will directly relate to using go as an automation language, but I'd rather learn the fundamentals before learning specialized examples.

[1]: http://www.golang-book.com/

https://gobyexample.com/ is also a great resource