Update README.md

README.md

@@ -154,3 +154,4 @@ A collective list of JSON APIs for use in web development.
 | API | Description | OAuth |Link |
 |---|---|---|---|
 | Church Calendar API | Catholic liturgical calendar | No | [Go!](http://calapi.inadiutorium.cz/) |
+| Non-working days API | Database of ICS files for non working days | No | [Go!](https://github.com/gadael/icsdb) |