Adding postupdate step recommended by documentation

see (https://docs.pixelfed.org/master/deployment.html)

seqs/pixelfed.sh

@@ -201,6 +201,18 @@ step_22() {
   exe php artisan user:create
 }
 
+step_24_info() { echo "Recommended post update procedure"; }
+step_24_alias() { ALIAS="postupdate"; }
+step_24() {
+  cd $toolPath
+  exe composer install --no-ansi --no-interaction --no-progress --no-scripts --optimize-autoloader
+  exe php artisan config:cache
+  exe php artisan route:cache
+  exe php artisan migrate --force
+  exe php artisan horizon:purge
+  exe php artisan storage:link
+}
+
 # Sequence Revision
 VERSION_SEQREV=3