doc/go1.16: add text/template changes to release notes

For #40700
Fixes #42914

Change-Id: I673d86a946c362e28bfbf35fab2c60ebfbd8bda2
Reviewed-on: https://go-review.googlesource.com/c/go/+/274472
Trust: Alberto Donizetti <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>

Author: ALTree

doc/go1.16.html

@@ -699,8 +699,9 @@ <h3 id="minor_library_changes">Minor changes to the library</h3>
 
 <dl id="text/template"><dt><a href="/pkg/text/template/">text/template</a></dt>
   <dd>
-    <p><!-- CL 254257 -->
-      TODO: <a href="https://golang.org/cl/254257">https://golang.org/cl/254257</a>: allow newlines inside action delimiters
+    <p><!-- CL 254257, golang.org/issue/29770 -->
+      Newlines characters are now allowed inside action delimiters,
+      permitting actions to span multiple lines.
     </p>
   </dd>
 </dl><!-- text/template -->