Add CoinGecko API (Cryptocurrency) (#850)

README.md

@@ -181,6 +181,7 @@ API | Description | Auth | HTTPS | CORS |
 | [Coinbase Pro](https://docs.pro.coinbase.com/#api) | Cryptocurrency Trading Platform | `apiKey` | Yes | Unknown |
 | [CoinBin](https://coinbin.org/) | Cryptocurrency information | No | Yes | Unknown |
 | [CoinDesk](http://www.coindesk.com/api/) | Bitcoin Price Index | No | No | Unknown |
+| [CoinGecko](http://www.coingecko.com/api) | Cryptocurrency Price, Market, and Developer/Social Data | No | Yes | Yes |
 | [Coinigy](https://coinigy.docs.apiary.io) | Interacting with Coinigy Accounts and Exchange Directly | `apiKey` | Yes | Unknown |
 | [CoinLayer](https://coinlayer.com) | Real-time Crypto Currency Exchange Rates | `apiKey` | Yes | Unknown |
 | [Coinlore](https://www.coinlore.com/cryptocurrency-data-api) | Cryptocurrencies prices, volume and more | No | Yes | Unknown |