[release-branch.go1.7] doc/devel/release.html: document go1.6.3 doesn't actually support macOS Sierra
[release-branch.go1.7] doc/devel/release.html: document go1.6.3 doesn't actually support macOS Sierra

Updates #17824.

Change-Id: I73cf89c21b418158c7014c3271cd1103a17a5c86
Reviewed-on: https://go-review.googlesource.com/32882
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>
Reviewed-on: https://go-review.googlesource.com/32885
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>
Reviewed-by: Minux Ma <72d850dbd8858b791995463d8539b5a379577f28@golang.org>

4ad/go,4ad/go,4ad/go,4ad/go,4ad/go,4ad/go,4ad/go,4ad/go