Update copyright date

Author: satterly

README.md

@@ -147,7 +147,7 @@ License
 -------
 
     Alerta monitoring system and console
-    Copyright 2012-2020 Nick Satterly
+    Copyright 2012-2023 Nick Satterly
 
     Licensed under the Apache License, Version 2.0 (the "License");
     you may not use this file except in compliance with the License.