Added README file

plugins/calendar/README

@@ -0,0 +1,18 @@
+A calendar module for Roundcube
+-------------------------------
+
+This plugin currently supports a local database as well as a Kolab groupware
+server as backends for calendar and event storage. For both drivers, some
+initialization of the local database is necessary. To do so, execute the
+SQL commands in drivers/<yourchoice>/SQL/<yourdatabase>.sql
+
+The client-side calendar UI relies on the 'fullcalenda'r project by Adam Arshaw
+with extensions made for the use in Roundcube. All changes are published in
+an official fork at https://github.com/roundcube/fullcalendar
+
+For recurring event computation, some utility classes from the Horde project
+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