Update 2014-07-19-demystifying-golangs-io-dot-reader-and-io-dot-writer-interfaces.markdown

Any type can satisfy an interface, not just a struct (as I am sure you know).  http://play.golang.org/p/FjNN7HcpMJ
Merge pull request #27 from ready4god2513/patch-2

Update 2014-07-19-demystifying-golangs-io-dot-reader-and-io-dot-writer-i...