doc/go1.11: link to module overview

Change-Id: Id381ee73e678ff4b025c1c35512a755ba49d6f81
Reviewed-on: https://go-review.googlesource.com/124702
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Andrew Bonventre <andybons@golang.org>

doc/go1.11.html

@@ -136,7 +136,8 @@ <h3 id="modules">Modules, package versioning, and dependency management</h3>
     NOTE: This is not present in go1.11beta1 but will be available in future
     betas and subsequent releases.
   </strong>
-  Go 1.11 adds experimental support for a new concept called “modules,”
+  <!-- TODO s;https://tip.golang.org;; for final release (right now golang.org/cmd/go doesn't have that section) -->
+  Go 1.11 adds preliminary support for a <a href="https://tip.golang.org/cmd/go/#hdr-Modules__module_versions__and_more">new concept called “modules,”</a>
   an alternative to GOPATH with integrated support for versioning and
   package distribution.
   Using modules, developers are no longer confined to working inside GOPATH,
@@ -155,10 +156,6 @@ <h3 id="modules">Modules, package versioning, and dependency management</h3>
   so we can fix them.
 </p>
 
-<p>
-  TODO: Link to intro doc.
-</p>
-
 <h3 id="importpath">Import path restriction</h3>
 
 <p>