message: Add comment on FirstWeekContainsDate type
diff: @@ -51,6 +51,13 @@ export type Day = 0 | 1 | 2 | 3 | 4 | 5 | 6
  export type Month = 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11
  +/**
  + * FirstWeekContainsDate is used to determine which week is the first week of the year, based on what day the January, 1 is in that week.
  + *
  + * The day in that week can only be 1 (Monday) or 4 (Thursday).
  + *
  + * Please see https://en.wikipedia.org/wiki/Week#Week_numbering for more information.
  + */
  export type FirstWeekContainsDate = 1 | 4
  export interface DateValues {
  