image: add a security considerations section to package doc
Internally the security model for the image package has always been,
if you don't call DecodeConfig before Decode, you cannot complain if
Decode attempts to create an arbitrarily large image (with the
assumption that DecodeConfig would've told you this information). This
should be explicitly documented.
Change-Id: I5c37b91131d6352637e725fe415f37a28f12f66d
Reviewed-on: https://go-review.googlesource.com/c/go/+/523578 Reviewed-by: Damien Neil <dneil@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>