doc: reflect {Num,}Method skips unexported methods

For #15673

Change-Id: I3ce8d4016854d41860c5a9f05a54cda3de49f337
Reviewed-on: https://go-review.googlesource.com/23430Reviewed-by: Ian Lance Taylor <iant@golang.org>

doc/go1.7.html

@@ -1049,6 +1049,16 @@ is like
 but distinguishes the tag not containing the given key
 from the tag associating an empty string with the given key.
 </p>
+
+<p>
+The
+<a href="/pkg/reflect/#Type.Method"><code>Method</code></a> and
+<a href="/pkg/reflect/#Type.NumMethod"><code>NumMethod</code></a>
+methods of
+<a href="/pkg/reflect/#Type"><code>Type</code></a> and
+<a href="/pkg/reflect/#Value"><code>Value</code></a>
+no longer return or count unexported methods.
+</p>
 </dd>
 
 <dl id="strings"><a href="/pkg/strings/">strings</a></dl>