Add What3Words (#2456)

README.md

@@ -797,6 +797,7 @@ API | Description | Auth | HTTPS | CORS |
 | [US ZipCode](https://smartystreets.com/docs/cloud/us-zipcode-api) | Validate and append data for any US ZipCode | `apiKey` | Yes | Yes |
 | [Utah AGRC](https://api.mapserv.utah.gov) | Utah Web API for geocoding Utah addresses | `apiKey` | Yes | Unknown |
 | [ViaCep](https://viacep.com.br) | Brazil RESTful zip codes API | No | Yes | Unknown |
+| [What3Words](https://w3w.co) | Three words as rememberable and unique coordinates worldwide | `apiKey` | Yes | Unknown |
 | [Yandex.Maps Geocoder](https://yandex.com/dev/maps/geocoder) | Use geocoding to get an object's coordinates from its address | `apiKey` | Yes | Unknown |
 | [ZipCodeAPI](https://www.zipcodeapi.com) | US zip code distance, radius and location API | `apiKey` | Yes | Unknown |
 | [Zippopotam.us](http://www.zippopotam.us) | Get information about place such as country, city, state, etc | No | No | Unknown |