add RIDB API(open data section) (#855)

* add RIDB API(open data section)

* Update README.md

README.md

@@ -564,6 +564,7 @@ API | Description | Auth | HTTPS | CORS |
 | [Microlink.io](https://microlink.io) | Extract structured data from any website | No | Yes | Yes |
 | [Population.io](http://api.population.io/) | Open demographic data such as population tables, population rank and life expectancy | No | No | Unknown |
 | [Quandl](https://www.quandl.com/) | Stock Market Data | No | Yes | Unknown |
+| [Recreation Information Database](https://ridb.recreation.gov/) | Recreational areas, federal lands, historic sites, museums, and other attractions/resources(US) | `apiKey` | Yes | Unknown |
 | [Scoop.it](http://www.scoop.it/dev) | Content Curation Service | `apiKey` | No | Unknown |
 | [Teleport](https://developers.teleport.org/) | Quality of Life Data | No | Yes | Unknown |
 | [Universities List](https://github.com/Hipo/university-domains-list) | University names, countries and domains | No | Yes | Unknown |