doc/go1.19: document loong64 port

Updates #46229
For #51400

Change-Id: Iedd5d3c4cd656b59ba2e1fe813851830849a8614
Reviewed-on: https://go-review.googlesource.com/c/go/+/410816
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Run-TryBot: David Chase <drchase@google.com>
Reviewed-by: Austin Clements <austin@google.com>

doc/go1.19.html

@@ -32,6 +32,9 @@ <h2 id="ports">Ports</h2>
 <p>
   TODO: complete this section, or delete if not needed
 </p>
+<p><!-- https://go.dev/issue/46229 -->
+  Go 1.19 supports the Loongson 64-bit architecture LoongArch on Linux (<code>GOOS=linux</code>, <code>GOARCH=loong64</code>).
+</p>
 
 <h2 id="tools">Tools</h2>
 <p>