doc/go1.16: add encoding/json note for tag change

For #40700
Fixes #42898

Change-Id: I652657ff8d6cce20bf868f0b1101d723d3f704d1
Reviewed-on: https://go-review.googlesource.com/c/go/+/274614
Trust: Joe Tsai <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>

Author: dsnet

doc/go1.16.html

@@ -456,7 +456,11 @@ <h3 id="minor_library_changes">Minor changes to the library</h3>
 <dl id="encoding/json"><dt><a href="/pkg/encoding/json/">encoding/json</a></dt>
   <dd>
     <p><!-- CL 234818 -->
-      TODO: <a href="https://golang.org/cl/234818">https://golang.org/cl/234818</a>: allow semicolon in field key / struct tag
+      The <code>json</code> struct field tags understood by
+      <a href="/pkg/encoding/json/#Marshal"><code>Marshal</code></a>,
+      <a href="/pkg/encoding/json/#Unmarshal"><code>Unmarshal</code></a>,
+      and related functionality now permit semicolon characters within
+      a JSON object name for a Go struct field.
     </p>
   </dd>
 </dl><!-- encoding/json -->