Add Calendarific (#2431)

README.md

@@ -262,6 +262,7 @@ API | Description | Auth | HTTPS | CORS |
 |---|---|---|---|---|
 | [Abstract Public Holidays](https://www.abstractapi.com/holidays-api) | Data on national, regional, and religious holidays via API | `apiKey` | Yes | Yes |
 | [Calendar Index](https://www.calendarindex.com/) | Worldwide Holidays and Working Days | `apiKey` | Yes | Yes |
+| [Calendarific](https://calendarific.com/) | Worldwide Holidays | `apiKey` | Yes | Unknown |
 | [Church Calendar](http://calapi.inadiutorium.cz/) | Catholic liturgical calendar | No | No | Unknown |
 | [Czech Namedays Calendar](https://svatky.adresa.info) | Lookup for a name and returns nameday date | No | No | Unknown |
 | [Festivo Public Holidays](https://docs.getfestivo.com/docs/products/public-holidays-api/intro) | Fastest and most advanced public holiday and observance service on the market | `apiKey` | Yes | Yes |