doc: add link to go command modules docs from Go 1.11 release notes

The FAQ already has a link to the release notes and the go command docs.
Add a link from the release notes to the go command docs, to ensure that
people ultimately end up there (the docs that then signpost
people to the relevant other help docs).

Updates #25517.

Change-Id: I284c84af712d4519c59f7ca6c396b05a4c967cee
Reviewed-on: https://go-review.googlesource.com/126777Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

doc/go1.11.html

@@ -148,7 +148,8 @@ Do not send CLs removing the interior tags from such phrases.
   to modules using Go 1.11 will continue to work with Go 1.12 and later.
   If you encounter bugs using modules,
   please <a href="https://golang.org/issue/new">file issues</a>
-  so we can fix them.
+  so we can fix them. For more information, see the
+  <a href="/cmd/go#hdr-Modules__module_versions__and_more"><code>go</code> command documentation</a>.
 </p>
 
 <h3 id="importpath">Import path restriction</h3>