doc: add release notes for reflect

Change-Id: I71a6816f54f8ad0f8531bb3f9de552fd136a0ed4
Reviewed-on: https://go-review.googlesource.com/c/go/+/181943
Reviewed-by: Ian Lance Taylor <[email protected]>

Author: julieqiu

doc/go1.13.html

@@ -291,11 +291,11 @@ <h3 id="minor_library_changes">Minor changes to the library</h3>
 <dl id="reflect"><dt><a href="/pkg/reflect/">reflect</a></dt>
   <dd>
     <p><!-- CL 171337 -->
-      TODO: <a href="https://golang.org/cl/171337">https://golang.org/cl/171337</a>: add Value.IsZero
+      The new <a href="/pkg/reflect/#Value.IsZero"><code>Value.IsZero</code></a> method reports whether a <code>Value</code> is a zero value for its type.
     </p>
 
     <p><!-- CL 174531 -->
-      TODO: <a href="https://golang.org/cl/174531">https://golang.org/cl/174531</a>: MakeFunc: allow assignment conversions on values returned from the wrapped function
+      The <a href="/pkg/reflect/#MakeFunc"><code>MakeFunc</code></a> function now allows assignment conversions on returned values, instead of requiring exact type match. This is particularly useful when the type being returned is an interface type, but the value actually returned  is a concrete value implementing that type.
     </p>
 
 </dl><!-- reflect -->