encoding/json: add example for json.HTMLEscape
encoding/json: add example for json.HTMLEscape

Change-Id: Ib00fcfd46eae27eea0a3d4cab4406f4c461fb57b
Reviewed-on: https://go-review.googlesource.com/c/160517
Reviewed-by: Andrew Bonventre <682ad9f487f614f19e8b7cc5d340bdc8e1c1b128@golang.org>
Run-TryBot: Andrew Bonventre <682ad9f487f614f19e8b7cc5d340bdc8e1c1b128@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

coreos/go-json