internal/history: document Go 1.16.1 and Go 1.15.9

Change-Id: I74784f4520661b580741ee3219a776cc17d6effd
Reviewed-on: https://go-review.googlesource.com/c/website/+/300589
Trust: Filippo Valsorda <filippo@golang.org>
Run-TryBot: Filippo Valsorda <filippo@golang.org>
Reviewed-by: Alexander Rakoczy <alex@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
diff --git a/internal/history/release.go b/internal/history/release.go
index a9cc3f4..e67f6b4 100644
--- a/internal/history/release.go
+++ b/internal/history/release.go
@@ -35,13 +35,13 @@
 		Date:     Date{2021, 3, 10},
 		Security: true,
 
-		Future: true,
+		Packages: []string{"archive/zip", "encoding/xml"},
 	},
 	{1, 15, 9}: {
 		Date:     Date{2021, 3, 10},
 		Security: true,
 
-		Future: true,
+		Packages: []string{"encoding/xml"},
 	},
 
 	{1, 16, 0}: {