Document example holidays

API.md

@@ -102,6 +102,28 @@ Holidays can be queried with `calendar.get_holidays`.
                         return true if it's a holiday and false if not.
                         Try to keep your calculations as simple as possible
 
+#### Examples
+```
+-- First day of every year
+calendar.register_holiday({
+	name = "New Year's Eve",
+	type = "monthday",
+	days = 0,
+	months = 0
+})
+
+-- First Sunday in May
+calendar.register_holiday({
+	name = "Mother's Day",
+	type = "custom",
+	is_holiday = function(total_days)
+		local d, m, y = calendar.get_date(total_days)
+		local wday = calendar.get_weekday(total_days)
+		return wday == 6 and m == 4 and d <= 6
+	end,
+})
+```
+
 ### `calendar.get_holidays(total_days)`
 Returns table of all holidays for the given day.