doc: document Go 1.11.12

Change-Id: I1b2e369befc58b3f88ac201442a2d9f76d87d54e
Reviewed-on: https://go-review.googlesource.com/c/go/+/185257Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>

doc/devel/release.html

@@ -168,6 +168,12 @@ See the <a href="https://github.com/golang/go/issues?q=milestone%3AGo1.11.11">Go
 1.11.11 milestone</a> on our issue tracker for details.
 </p>
 
+<p>
+go1.11.12 (released 2019/07/08) includes fixes to the compiler and the linker.
+See the <a href="https://github.com/golang/go/issues?q=milestone%3AGo1.11.12">Go
+1.11.12 milestone</a> on our issue tracker for details.
+</p>
+
 <h2 id="go1.10">go1.10 (released 2018/02/16)</h2>
 
 <p>