`bytes` and `strings` are pretty similar to each other, this commit
brings `strings` examples to its counter-part.

Partially addresses #16360

Change-Id: I551320eaa78be9df69012035f1c3333f500e04c9
Reviewed-on: https://go-review.googlesource.com/25062Reviewed-by: Andrew Gerrand <adg@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>