doc: describe golang.org/x/go/packages in go1.11 release notes
doc: describe golang.org/x/go/packages in go1.11 release notes

Also, rename an HTML element ID to avoid duplicate.

Fixes golang/go#27038

Change-Id: Icc064a1cc86ddc794fc085d98b4cde3effff8ad0
Reviewed-on: https://go-review.googlesource.com/129635
Reviewed-by: Andrew Bonventre <682ad9f487f614f19e8b7cc5d340bdc8e1c1b128@golang.org>
Reviewed-by: Ian Cottrell <52376736e5e84615ec49f9c1843b8acc178b1d8d@google.com>

CAFxX/go,akutz/go,akutz/go,golang/go,nawawi/go,golang/go,CAFxX/go,josharian/go,golang/go,akutz/go,cloudflare/go,nawawi/go,cloudflare/go,josharian/go,josharian/go,nawawi/go,josharian/go,cloudflare/go,nawawi/go,nawawi/go,CAFxX/go,golang/go,josharian/go,nawawi/go,CAFxX/go,akutz/go,josharian/go,CAFxX/go,CAFxX/go,akutz/go,golang/go,cloudflare/go,akutz/go,CAFxX/go,josharian/go,akutz/go,golang/go,nawawi/go,nawawi/go,cloudflare/go,golang/go,cloudflare/go,cloudflare/go,cloudflare/go,josharian/go,CAFxX/go,akutz/go,golang/go