Heads up: Consider go-package.mk deprecated

[Benny Siegert <bsiegert%gmail.com@localhost>]

Hi!

I just added a notice to lang/go/go-package.mk that it should not be
used for new packages. Instead, prefer module-based builds with
go-module.mk. The GOPATH-based builds implemented by go-package.mk
will eventually go away.

If you maintain a package for a program written in Go, and it contains
a "go.mod" at the top level, please switch it to modules.

Eventually, this will allow us to remove a ton of intermediate
"library" packages for Go, as they are no longer needed with module
builds.

-- 
Benny