Cookbook example showing how to handle iCalendar time zones

TODO: make sure it works

Author: ptomato

docs/cookbook-icalendar-time-zone.md

@@ -0,0 +1,9 @@
+# Example of custom time zones with iCalendar data
+
+The iCalendar data format allows specifying custom rules for time zone UTC offset changes.
+Using the Temporal API directly, you can only make `Temporal.ZonedDateTime` instances with time zones that are available in your JS environment's version of the time zone database.
+However, you can make a custom `ZonedDateTime` class that allows performing calculations with a custom time zone based on iCalendar rules.
+
+```javascript
+{{cookbook/icalendarTimeZones.mjs}}
+```

docs/cookbook.md

@@ -575,3 +575,10 @@ This calendar is currently not built in to JS environments.
 This serves as an example of how to build support for calendars that are not widespread in browsers.
 
 → [Nepali calendar](cookbook-nepali-calendar.md)
+
+### Custom time zone rules with iCalendar data
+
+Use Temporal to perform time zone calculations with time zones not in the time zone database.
+The iCalendar data format allows specifying custom rules for time zone UTC offset changes.
+
+→ [iCalendar time zones](cookbook-icalendar-time-zone.md)