Add Ducks Unlimited (#2756)

README.md

@@ -797,6 +797,7 @@ API | Description | Auth | HTTPS | CORS |
 | [CitySDK](http://www.citysdk.eu/citysdk-toolkit/) | Open APIs for select European cities | No | Yes | Unknown |
 | [Country](http://country.is/) | Get your visitor's country from their IP | No | Yes | Yes |
 | [CountryStateCity](https://countrystatecity.in/) | World countries, states, regions, provinces, cities & towns in JSON, SQL, XML, YAML, & CSV format | `apiKey` | Yes | Yes |
+| [Ducks Unlimited](https://gis.ducks.org/datasets/du-university-chapters/api) | API explorer that gives a query URL with a JSON response of locations and cities | No | Yes | No | 
 | [FreeGeoIP](https://freegeoip.app/) | Free geo ip information, no registration required. 15k/hour rate limit | No | Yes | Yes |
 | [GeoApi](https://api.gouv.fr/api/geoapi.html) | French geographical data | No | Yes | Unknown |
 | [Geoapify](https://www.geoapify.com/api/geocoding-api/) | Forward and reverse geocoding, address autocomplete | `apiKey` | Yes | Yes |