[release-branch.go1.7] doc: document go1.7.4 and go1.6.4
[release-branch.go1.7] doc: document go1.7.4 and go1.6.4

Change-Id: I0728afe6a1d1e0aee4701e51a5548fa9fd637b66
Reviewed-on: https://go-review.googlesource.com/33795
Reviewed-by: Russ Cox <5ad239cb8a44f659eaaee0aa1ea5b94947abe557@golang.org>
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>
Reviewed-on: https://go-review.googlesource.com/33796
Reviewed-by: Chris Broadfoot <0c2851a4f8ab4aa5606e69c0757771dd13dbe686@golang.org>

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