doc/go1.17: require macOS 10.13 or later

For #44513.
For #23011.

Change-Id: Ic092e38da3601a43d7e2110f500db4a6a6f845f5
Reviewed-on: https://go-review.googlesource.com/c/go/+/316889
Trust: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Alexander Rakoczy <alex@golang.org>
Reviewed-by: Carlos Amedee <carlos@golang.org>

doc/go1.17.html

@@ -31,8 +31,16 @@ <h2 id="language">Changes to the language</h2>
 
 <h2 id="ports">Ports</h2>
 
+<h3 id="darwin">Darwin</h3>
+
+<p><!-- golang.org/issue/23011 -->
+  As <a href="go1.16#darwin">announced</a> in the Go 1.16 release
+  notes, Go 1.17 requires macOS 10.13 High Sierra or later; support
+  for previous versions has been discontinued.
+</p>
+
 <p>
-  TODO: complete this section, or delete if not needed
+  TODO: complete the Ports section
 </p>
 
 <h2 id="tools">Tools</h2>