Document how to reverse sort order

Author: Lenbok

README.org

@@ -44,6 +44,14 @@ Launch =time-zones= with:
     :vc (:url "https://github.com/xenodium/time-zones"))
 #+end_src
 
+** Customization
+
+The default sort order is chronologically increasing, so time zones in "the past" occur earlier in the list than time zones in "the future". You can reverse the sorting via:
+
+#+begin_src emacs-lisp :lexical no
+  (advice-add 'time-zones--sort-cities-by-time :filter-return 'reverse)
+#+end_src
+
 * Run
 
 #+begin_src