UPDATE: copyright year

Author: fileformat

docs/_includes/footer.html

@@ -1,7 +1,7 @@
         <footer class="container hidden-print">
             <hr/>
             <p class="small text-muted text-center">
-                Copyright &copy; 2023<!-- COPYRIGHTYEAR --> by <a href="https://andrew.marcuse.info/contact.html">Andrew Marcuse</a>
+                Copyright &copy; 2023-2024<!-- COPYRIGHTYEAR --> by <a href="https://andrew.marcuse.info/contact.html">Andrew Marcuse</a>
                 <!-- LATER: github link -->
                 <!-- LATER: FFI link -->
                 <!-- LATER: DRS link -->