_content/doc/go1.18: mention net/http IDNA change

Based on CL 366955 originally by Timothy Gu.

For golang/go#46001
For golang/go#47694

Change-Id: Ide7711680d651c4cbbb6da13ab33b67cf5e26758
Reviewed-on: https://go-review.googlesource.com/c/website/+/389955
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Trust: DO NOT USE <iant@google.com>

_content/doc/go1.18.html

@@ -1093,6 +1093,18 @@ <h3 id="minor_library_changes">Minor changes to the library</h3>
       <code>ResponseWriter</code> and <code>Request.Body</code> with a
       <a href="/pkg/net/http#MaxBytesReader"><code>MaxBytesReader</code></a>.
     </p>
+
+    <p><!-- CL 359634, CL 360381, CL 362735 -->
+      When looking up a domain name containing non-ASCII characters,
+      the Unicode-to-ASCII conversion is now done in accordance with
+      Nontransitional Processing as defined in the
+      <a href="https://unicode.org/reports/tr46/">Unicode IDNA
+      Compatibility Processing</a> standard (UTS #46). The
+      interpretation of four distinct runes are changed: ß, ς,
+      zero-width joiner U+200D, and zero-width non-joiner
+      U+200C. Nontransitional Processing is consistent with most
+      applications and web browsers.
+    </p>
   </dd>
 </dl><!-- net/http -->