doc: document Go 1.13.4

Change-Id: Ib29e642c56eca96826187f5737d74f8c0430ac3d
Reviewed-on: https://go-review.googlesource.com/c/go/+/204638
Run-TryBot: Andrew Bonventre <andybons@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Katie Hockman <katie@golang.org>

doc/devel/release.html

@@ -54,6 +54,15 @@ See the <a href="https://github.com/golang/go/issues?q=milestone%3AGo1.13.3">Go
 1.13.3 milestone</a> on our issue tracker for details.
 </p>
 
+<p>
+go1.13.4 (released 2019/10/31) includes fixes to the <code>net/http</code> and
+<code>syscall</code> packages. It also fixes an issue on macOS 10.15 Catalina
+where the non-notarized installer and binaries were being
+<a href="https://golang.org/issue/34986">rejected by Gatekeeper</a>.
+See the <a href="https://github.com/golang/go/issues?q=milestone%3AGo1.13.4">Go
+1.13.4 milestone</a> on our issue tracker for details.
+</p>
+
 <h2 id="go1.12">go1.12 (released 2019/02/25)</h2>
 
 <p>