_content/doc/comment: add note about conflicting package imports
_content/doc/comment: add note about conflicting package imports

When multiple source files import different packages to the same name,
that creates an ambiguity, disallowing the use of the short package name
in doc comment links.

For golang/go#51082.

Change-Id: Id46ca1e2db2c681e02ed34fc4dd57e3e43030994
Reviewed-on: https://go-review.googlesource.com/c/website/+/414694
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@google.com>
Run-TryBot: Russ Cox <5ad239cb8a44f659eaaee0aa1ea5b94947abe557@golang.org>
TryBot-Result: Gopher Robot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

golang/website,golang/website,golang/website,golang/website,golang/website,golang/website,golang/website