unicode/utf8: document the handling of runes out of range in EncodeRune
Document the way EncodeRune currently handles runes which are
out of range. Also add an example showing that behaviour.
Change-Id: I0f8e7645ae053474ec319085a2bb6d7f73bc137c
Reviewed-on: https://go-review.googlesource.com/c/go/+/255998 Reviewed-by: Rob Pike <r@golang.org> Reviewed-by: Giovanni Bajo <rasky@develer.com>
Trust: Giovanni Bajo <rasky@develer.com>
Run-TryBot: Giovanni Bajo <rasky@develer.com>
TryBot-Result: Go Bot <gobot@golang.org>