This is an attempt to clarify the "advice" section of the package docs a
little bit and encourage a specific style of use for weak structures.
It's not perfect, but it's something.
Change-Id: Id84b76d207619cc2e78439c5c903ec9575199734
Reviewed-on: https://go-review.googlesource.com/c/go/+/633675
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Carlos Amedee <carlos@golang.org>
Auto-Submit: Michael Knyszek <mknyszek@google.com>