Add additional info regarding timestamp fields (#4456)

* Add additional info regarding timestamp fields

Added a note on Iterable's date field in our document on Iterable destination. Iterable has a specific date format that must be used to segment a field by date. Thus, Segment converts ISO strings to UTC before sending it to iterable.

We have had tickets on this issue where a customer is confused as why the timestamp is getting converted to UTC despite sending the local time.

* Apply suggestions from code review

Co-authored-by: stayseesong <83784848+stayseesong@users.noreply.github.com>

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Co-authored-by: markzegarelli <mark.zegarelli@segment.com>
Co-authored-by: stayseesong <83784848+stayseesong@users.noreply.github.com>

Author: 3 people

src/connections/destinations/catalog/iterable/index.md

@@ -70,6 +70,9 @@ First `track` event with `userId` and `email`; user will be created
 
 Subsequent `track` with `userId`
 
+> info ""
+> If you send an ISO formatted date field in your events, Segment converts it into UTC to conform to standard Iterable format: `yyyy-MM-dd HH:mm:ss ZZ` (for example, `2023-02-05 20:42:10 +00:00`). Iterable has a specific date format that must be used to segment a field by date. Read more about Iterable date field [here](https://support.iterable.com/hc/en-us/articles/208183076-Data-Field-Types-in-Iterable#date){:target="_blank"}.
+
 ### Ecommerce
 
 Iterable also supports Segment's [ecommerce events](/docs/connections/spec/ecommerce/v2/). This works just as you would expect, using the `track` method.