doc/go1.16: add runtime/debug changes to release notes

For #40700
Fixes #42912

Change-Id: Ifd36950136db1fc93a8de76a2717a473210418b1
Reviewed-on: https://go-review.googlesource.com/c/go/+/274473
Trust: Alberto Donizetti <[email protected]>
Reviewed-by: Keith Randall <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>

Author: ALTree

doc/go1.16.html

@@ -663,7 +663,10 @@ <h3 id="minor_library_changes">Minor changes to the library</h3>
 <dl id="runtime/debug"><dt><a href="/pkg/runtime/debug/">runtime/debug</a></dt>
   <dd>
     <p><!-- CL 249677 -->
-      TODO: <a href="https://golang.org/cl/249677">https://golang.org/cl/249677</a>: provide Addr method for errors from SetPanicOnFault
+      The <a href="/pkg/runtime#Error"><code>runtime.Error</code> values
+      used when <code>SetPanicOnFault</code> is enabled may now have an
+      <code>Addr</code> method. If that method exists, it returns the memory
+      address that triggered the fault.
     </p>
   </dd>
 </dl><!-- runtime/debug -->