content/static/doc: link module blog posts from golang.org/doc

Updates golang/go#33637

Change-Id: I37c81d2358c9b2c7ae11939b3884acea2612ff7d
Reviewed-on: https://go-review.googlesource.com/c/website/+/197640
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>

cmd/golangorg/regtest_test.go

@@ -34,6 +34,10 @@ func TestLiveServer(t *testing.T) {
 		PostBody    string
 		StatusCode  int // if 0, expect 2xx status code.
 	}{
+		{
+			Path:      "/doc/",
+			Substring: "an introduction to using modules in a simple project",
+		},
 		{
 			Path:      "/doc/faq",
 			Substring: "What is the purpose of the project",

content/static/doc/docs.html

@@ -168,6 +168,13 @@ <h4>Packages</h4>
 <li><a href="/blog/go-image-package">The Go image package</a> - the fundamentals of the <a href="/pkg/image/">image</a> package.</li>
 <li><a href="/blog/go-imagedraw-package">The Go image/draw package</a> - the fundamentals of the <a href="/pkg/image/draw/">image/draw</a> package.</li>
 </ul>
+
+<h4>Modules</h4>
+<ul>
+<li><a href="/blog/using-go-modules">Using Go Modules</a> - an introduction to using modules in a simple project.</li>
+<li><a href="/blog/migrating-to-go-modules">Migrating to Go Modules</a> - converting an existing project to use modules.</li>
+<li><a href="/blog/publishing-go-modules">Publishing Go Modules</a> - how to make new versions of modules available to others.</li>
+</ul>
 {{end}}
 
 <h4>Tools</h4>