doc/go1.20.html: pre-announce dropping Windows 7, 8, and friends

For #57003, #57004.

Change-Id: Ic1386a0ce83897411fbc68c83a9125af1cc11b54
Reviewed-on: https://go-review.googlesource.com/c/go/+/457695
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Auto-Submit: Heschi Kreinick <heschi@google.com>
Run-TryBot: Heschi Kreinick <heschi@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

doc/go1.20.html

@@ -67,9 +67,16 @@ <h2 id="language">Changes to the language</h2>
 
 <h2 id="ports">Ports</h2>
 
+<h3 id="windows">Windows</h3>
+
+<p><!-- https://go.dev/issue/57003, https://go.dev/issue/57004 -->
+  Go 1.20 is the last release that will run on any release of Windows 7, 8, Server 2008 and Server 2012.
+  Go 1.21 will require at least Windows 10 or Server 2016.
+</p>
+
 <h3 id="darwin">Darwin and iOS</h3>
 
-<p><!-- golang.org/issue/23011 -->
+<p><!-- https://go.dev/issue/23011 -->
   Go 1.20 is the last release that will run on macOS 10.13 High Sierra or 10.14 Mojave.
   Go 1.21 will require macOS 10.15 Catalina or later.
 </p>