cmd/googlegolangorg: add google.golang.org/open2opaque redirect

Change-Id: I44e86f64ca742a0387bf5f6a449fc8c86ec1bb86
Reviewed-on: https://go-review.googlesource.com/c/website/+/636615
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Carlos Amedee <carlos@golang.org>
Reviewed-by: Carlos Amedee <carlos@golang.org>
Auto-Submit: Michael Stapelberg <stapelberg@google.com>

cmd/googlegolangorg/main.go

@@ -41,6 +41,11 @@ var repoMap = map[string]Repo{
 		URL: "https://go.googlesource.com/protobuf",
 		Src: github("protocolbuffers/protobuf-go"),
 	},
+	"open2opaque": {
+		VCS: "git",
+		URL: "https://go.googlesource.com/open2opaque",
+		Src: github("golang/open2opaque"),
+	},
 }
 
 // Repo represents a repository containing Go code.