Make the role of "leap seconds" more obvious in DateTime and Instant #3881
Description
There was a question on Facebook where the poster was surprised that for a range of given date times the DateTime.Instant.Int varied from the perl DateTime->epoch by an increasing amount.
Having looked at the documentation pages for both DateTime and Instant there doesn't appear to be anywhere where it is made explicit that leap seconds are in play at all, apart from the discussion of "Future Leap Seconds" in the Instant page.
It would probably be useful to have some introductory text in both DateTime and Instant that describes the role of the "leap seconds" and possibly also in the methods such as .posix which return the number of seconds describe why, due to the leap seconds, they will differ from .Instance.Int.
Haven't got any particular suggestions as to what the words should be.