added PHP 8.3 migration guide link (#101)

Author: mumumu

manual.xml.in

@@ -435,6 +435,7 @@
  <book xml:id="appendices">
   <title>&Appendices;</title>
   &appendices.history;
+  &appendices.migration83;
   &appendices.migration82;
   &appendices.migration81;
   &appendices.migration80;