Note leap month behavior (#7765)

Leftover note from Markus' review


## Changelog: N/A

Author: Manishearth

components/calendar/src/types.rs

@@ -475,6 +475,10 @@ impl fmt::Display for MonthCode {
 /// * `Month::new(7)` = `M07`
 /// * `Month::leap(2)` = `M02L`
 ///
+/// Note that in Temporal's model, "leap month 2" (M02L) means the month that occurs after the
+/// non-leap month numbered 2 (M02), even if the calendar considers the month to be a variant of
+/// the subsequent month.
+///
 /// [Temporal]: https://tc39.es/proposal-intl-era-monthcode/
 #[derive(Copy, Clone, Debug, PartialEq, Hash, Eq, PartialOrd)]
 pub struct Month {