Added Practical Cryptography With Go

In a "Go" section

free-programming-books.md

@@ -834,6 +834,7 @@
 * [Learning Go](http://archive.miek.nl/projects/learninggo/index.html)
 * [Network programming with Go](http://jan.newmarch.name/go/)
 * [The Go Tutorial](http://golang.org/doc/go_tutorial.html)
+* [Practical Cryptography With Go](https://leanpub.com/gocrypto/read)
 
 
 ###Gradle