doc: document Go 1.13.3

Change-Id: Ia571b8aa791578a77ed5c2b8eaf45c9684eea1c3
Reviewed-on: https://go-review.googlesource.com/c/go/+/201820Reviewed-by: Andrew Bonventre <andybons@golang.org>

doc/devel/release.html

@@ -46,6 +46,14 @@ See the <a href="https://github.com/golang/go/issues?q=milestone%3AGo1.13.2">Go
 1.13.2 milestone</a> on our issue tracker for details.
 </p>
 
+<p>
+go1.13.3 (released 2019/10/17) includes fixes to the go command,
+the toolchain, the runtime, <code>syscall</code>, <code>net</code>,
+<code>net/http</code>, and <code>crypto/ecdsa</code> packages.
+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>
+
 <h2 id="go1.12">go1.12 (released 2019/02/25)</h2>
 
 <p>