Add documentation about timezone fix in iCal parser

plugins/calendar/README

@@ -16,6 +16,8 @@ are used. They are packaged in a slightly modified version with this plugin.
 iCalendar parsing is done with the help of the Horde_iCalendar class. A copy
 of that class with all its dependencies is part of this package. In order
 to update it, execute lib/get_horde_icalendar.sh > lib/Horde_iCalendar.php
+Finally apply the patch lib/Horde_iCalendar_timezone.diff to fix timezone
+handling when parsing iCal files.
 
 IMPORTANT
 ---------

plugins/calendar/lib/Horde_iCalendar_timezone.diff

@@ -1,7 +1,7 @@
 diff --git a/plugins/calendar/lib/Horde_iCalendar.php b/plugins/calendar/lib/Horde_iCalendar.php
 index a3ff79d..6d75d27 100644
---- a/plugins/calendar/lib/Horde_iCalendar.php
-+++ b/plugins/calendar/lib/Horde_iCalendar.php
+--- a/lib/Horde_iCalendar.php
++++ b/lib/Horde_iCalendar.php
 @@ -1874,7 +1874,17 @@ class Horde_iCalendar {
      {
          $vtimezone = $this->_container->findComponentByAttribute('vtimezone', 'TZID', $tzid);