doc: add Code of Conduct

Fixes #13073

Change-Id: I4fd9c6c61f1b9d49f66816839ca35209b4147ae3
Reviewed-on: https://go-review.googlesource.com/17167
Reviewed-by: Russ Cox <rsc@golang.org>
diff --git a/doc/contrib.html b/doc/contrib.html
index b3ca155..31bb0a4 100644
--- a/doc/contrib.html
+++ b/doc/contrib.html
@@ -91,10 +91,16 @@
 
 <p>
 Security-related issues should be reported to
-<a href="mailto:security@golang.org">security@golang.org</a>.
+<a href="mailto:security@golang.org">security@golang.org</a>.<br>
 See the <a href="/security">security policy</a> for more details.
 </p>
 
+<p>
+Community-related issues should be reported to
+<a href="mailto:conduct@golang.org">conduct@golang.org</a>.<br>
+See the <a href="/conduct">Code of Conduct</a> for more details.
+</p>
+
 <h3><a href="/doc/contribute.html">Contributing code</a></h3>
 
 <p>