add Trefle API (#1076)

README.md

@@ -712,6 +712,7 @@ API | Description | Auth | HTTPS | CORS |
 | [SHARE](https://share.osf.io/api/v2/) | A free, open, dataset about research and scholarly activities | No | Yes | Unknown |
 | [SpaceX](https://github.com/r-spacex/SpaceX-API) | Company, vehicle, launchpad and launch data | No | Yes | Unknown |
 | [Sunrise and Sunset](https://sunrise-sunset.org/api) | Sunset and sunrise times for a given latitude and longitude | No | Yes | Unknown |
+| [Trefle](https://trefle.io/) | Botanical data for plant species | `apiKey` | Yes | Unknown |
 | [USGS Earthquake Hazards Program](https://earthquake.usgs.gov/fdsnws/event/1/) | Earthquakes data real-time | No | Yes | Unknown |
 | [USGS Water Services](https://waterservices.usgs.gov/) | Water quality and level info for rivers and lakes | No | Yes | Unknown |
 | [World Bank](https://datahelpdesk.worldbank.org/knowledgebase/topics/125589) | World Data | No | No | Unknown |