[x/blog] content: add missing summaries

Also remove spurious time in godoc.org-redirect.article.
It was copy-pasted from pkgsite-redesign.article, which needed it
because we posted two blog posts together, and the times
in 11years.article and pkgsite-redesign.article decided the
order in which they appeared on the blog.
But in general times are unnecessary, so remove the
one in godoc.org-redirect.article to avoid future copy-pasting.

Change-Id: I43e43baf911155d8f8e5fbc77110d4ede836518e
Reviewed-on: https://go-review.googlesource.com/c/blog/+/278933
Trust: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>
X-Blog-Commit: 429a8530ad5b2e44df336470d64300336d01a82d
diff --git a/blog/content/11years.article b/blog/content/11years.article
index 97943f7..1c2188f 100644
--- a/blog/content/11years.article
+++ b/blog/content/11years.article
@@ -1,5 +1,6 @@
 # Eleven Years of Go
 12:01 10 Nov 2020
+Summary: Happy Birthday, Go!
 
 Russ Cox, for the Go team
 
diff --git a/blog/content/godoc.org-redirect.article b/blog/content/godoc.org-redirect.article
index e3d7d33..c7183e0 100644
--- a/blog/content/godoc.org-redirect.article
+++ b/blog/content/godoc.org-redirect.article
@@ -1,5 +1,6 @@
 # Redirecting godoc.org requests to pkg.go.dev
-12:00 15 Dec 2020
+15 Dec 2020
+Summary: The plan for moving from godoc.org to pkg.go.dev.
 
 Julie Qiu
 
diff --git a/blog/content/pkgsite-redesign.article b/blog/content/pkgsite-redesign.article
index bb9658b..db22bff 100644
--- a/blog/content/pkgsite-redesign.article
+++ b/blog/content/pkgsite-redesign.article
@@ -1,5 +1,6 @@
 # Pkg.go.dev has a new look!
 12:00 10 Nov 2020
+Summary: Announcing a new user experience on pkg.go.dev.
 
 Julie Qiu