Add a timezone guide for DST jumps at midnight

guides/moment-timezone/01-data-calculations/03-dst-jumps.md

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+---
+title: Timing of DST Jumps
+---
+
+Time zones that use daylight saving time (DST) vary about when they implement the time jumps.
+You shouldn't assume that the rules you're familiar with from a local time zone translate to other zones.
+
+One difference that often catches out developers is that some zones change clocks at midnight.
+A good example comes from Jordan (`Asia/Amman`) in 2021:
+
+* One second after `2021-03-25 23:59:59` was `2022-03-26 01:00:00` (DST started).
+* One second after `2021-10-29 00:59:59` was `2022-10-29 00:00:00` (DST stopped).
+
+This creates the situation where midnight at the start of March 26 **didn't happen**, while midnight on October 29 happened twice.
+
+Moment Timezone accounts for these oddities as described in the ["Parsing Ambiguities" documentation](/timezone/docs/#/using-timezones/parsing-ambiguous-inputs/).
+But applications can still have bugs when they make other assumptions about time jumps, especially regarding the start of a day.
+So be aware that **a day doesn't always start at midnight**.