Create subsections in the CHANGELOG

fix #3374

CHANGELOG.rst

 Version 9.0
 ===========
 
-- SIGHUP is now caught and reloads the configuration like SIGUSR1 and 2.
+For users
+---------
+- Messages reflections are now properly cut if the body was cut before
+  being to sent to IRC
 - Messages from unjoined resources are now rejected instead of being accepted.
   This helps clients understand that they are not in the room (because of
   some connection issue for example).
 - All commands sent to IRC servers are now throttled to avoid being
   disconnected for excess flood. The limit value can be customized using the
   ad-hoc configuration form on a server JID.
+
+For admins
+----------
+- SIGHUP is now caught and reloads the configuration like SIGUSR1 and 2.
 - Add a verify_certificate policy option that lets the admin disable
   certificate validation per-domain.
-- Messages reflections are now properly cut if the body was cut before
-  being to sent to IRC
 
 Version 8.3 - 2018-06-01
 ========================