doc: update link to self-hosted "The Laws of Reflection" article

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/5717046

doc/go_faq.html

@@ -756,7 +756,7 @@ Similar situations to those described here can arise whenever interfaces are use
 Just keep in mind that if any concrete value
 has been stored in the interface, the interface will not be <code>nil</code>.
 For more information, see
-<a href="http://blog.golang.org/2011/09/laws-of-reflection.html">this blog post</a>.
+<a href="/doc/articles/laws_of_reflection.html">The Laws of Reflection</a>.
 </p>