Add icalendar-compatibility

This adds https://icalendar-compatibility.readthedocs.io/en/latest/ as a related project.

README.rst

@@ -178,6 +178,7 @@ Related projects
 * `recurring-ical-events <https://pypi.org/project/recurring-ical-events/>`_. Library to query an ``icalendar.Calendar`` object for events and other components happening at a certain date or within a certain time.
 * `x-wr-timezone <https://pypi.org/project/x-wr-timezone/>`_. Library and command line tool to make ``icalendar.Calendar`` objects and files from Google Calendar (using the non-standard ``X-WR-TIMEZONE`` property) compliant with the standard (:rfc:`5545`).
 * `ics-query <http://pypi.org/project/ics-query>`_. Command line tool to query iCalendar files for occurrences of events and other components.
+* `icalendar-compatibility <https://icalendar-compatibility.readthedocs.io/en/latest/>`_ - access to event data compatible with RFC5545 and different implementations
 
 Further Reading
 ===============