solutions: Add solution for Readers exercise
solutions: Add solution for Readers exercise

The solution to this exercise was missing.

Fixes golang/tour#34

Change-Id: Ic416ab207a0acc9f196803f4df4497a36ea3d702
Reviewed-on: https://go-review.googlesource.com/34957
Reviewed-by: Joe Tsai <7277d7402195d5c2006c89f45718cf82bb3e527f@gmail.com>

zorion/go-tour-ca,shuLhan/go-tour-id,shuLhan/tour,shuLhan/tour,dupoxy/go-tour-fr,dupoxy/go-tour-fr,Go-zh/tour,shuLhan/go-tour-id,golang/tour,Go-zh/tour,Go-zh/tour,shuLhan/go-tour-id,golians/tour,Go-zh/tour,dupoxy/go-tour-fr,golians/tour,golians/tour,zorion/go-tour-ca,shuLhan/tour