math: add Remainder example
math: add Remainder example

Change-Id: I4b0fa69a36b04103473aa08e246fa193315ac5aa
Reviewed-on: https://go-review.googlesource.com/c/go/+/353689
Reviewed-by: Emmanuel Odeke <bd234ba4276433f0e5fc7a8fa2d18274fa711567@orijtech.com>
Reviewed-by: Robert Griesemer <a6752097faebf1f02d80107d77a9be009089afe3@golang.org>
Run-TryBot: Emmanuel Odeke <bd234ba4276433f0e5fc7a8fa2d18274fa711567@orijtech.com>
TryBot-Result: Go Bot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

golang/go,cloudflare/go,nawawi/go,CAFxX/go,golang/go,CAFxX/go,nawawi/go,cloudflare/go,cloudflare/go,cloudflare/go,CAFxX/go,nawawi/go,cloudflare/go,nawawi/go,nawawi/go,CAFxX/go,golang/go,cloudflare/go,CAFxX/go,CAFxX/go,nawawi/go,golang/go,nawawi/go,golang/go,cloudflare/go,golang/go,nawawi/go,golang/go,golang/go,CAFxX/go,cloudflare/go,CAFxX/go