[master] ae98a60fd correctly document event_function change

[Nils Goroll]

commit ae98a60fd09c83e85d76c0f2eaadc705816f57d9
Author: Nils Goroll <nils.goroll at uplex.de>
Date:   Sat Feb 2 14:59:29 2019 +0100

    correctly document event_function change
    
    my previous commit 7767fc32a368439915086f26ef99cf6aae578484 was
    incaccurate
    
    Ref d8ae26b5a0b4a1102360a61a145e4730e52d68bc

diff --git a/doc/changes.rst b/doc/changes.rst
index c7c690b1c..fca592c34 100644
--- a/doc/changes.rst
+++ b/doc/changes.rst
@@ -101,10 +101,13 @@ C APIs (for vmod and utility authors)
 * Varnish-based tools using the VUT interface should now consider
   using the ``VUT_Usage()`` function for consistency
 
-* The `event_function` callback for VCL events in vmods used to have
-  the fixed name ``event_function`` and has now been renamed to
-  `$Prefix`\ ``event_function`` if `$Prefix` is defined in the
-  ``.vcc`` files or ``vmod_event_function`` by default
+* The name of the `event_function` callback for VCL events in vmods is
+  now prefixed by `$Prefix`\ ``_``\ ` if `$Prefix` is defined in the
+  ``.vcc`` file, or ``vmod_`` by default.
+
+  So, for example, with ``$Event foo`` and no `$Prefix`, the event
+  function will be called ``vmod_foo`` and with ``$Prefix bar`` it
+  will be called ``bar_foo``.
 
 Fixed bugs
 ----------