Update CalendarEvent timezone requirements (#1709)

Author: allenporter

docs/core/entity/calendar.md

@@ -122,8 +122,8 @@ A `CalendarEvent` represents an individual event on a calendar.
 
 | Name        | Type             | Default      | Description                                                                                                                                     |
 | ----------- | ---------------- | ------------ | ----------------------------------------------------------------------------------------------------------------------------------------------- |
-| start       | datetime or date | **Required** | The start (inclusive) of the event. Must be before `end`. Both `start` and `end` must be the same type. As a datetime, must be in UTC timezone. |
-| end         | datetime or date | **Required** | The end (exclusive) of the event. Must be after `start`. As a datetime, must be in UTC timezone.                                                |
+| start       | datetime or date | **Required** | The start (inclusive) of the event. Must be before `end`. Both `start` and `end` must be the same type. As a datetime, must have a timezone.    |
+| end         | datetime or date | **Required** | The end (exclusive) of the event. Must be after `start`. As a datetime, must have a timezone that is the same as start.                         |
 | summary     | string           | **Required** | A title or summary of the event.                                                                                                                |
 | location    | string           | `None`       | A geographic location of the event.                                                                                                             |
 | description | string           | `None`       | A detailed description of the event.                                                                                                            |