Add Kraken (#2139)

README.md

@@ -317,6 +317,7 @@ API | Description | Auth | HTTPS | CORS |
 | [CryptoTradingAPI](https://www.cryptotradingapi.io/) | Crypto Prices & Technical Indicators | `apiKey` | Yes | Unknown |
 | [Gemini](https://docs.gemini.com/rest-api/) | Cryptocurrencies Exchange | No | Yes | Unknown |
 | [ICObench](https://icobench.com/developers) | Various information on listing, ratings, stats, and more | `apiKey` | Yes | Unknown |
+| [Kraken](https://docs.kraken.com/rest/) | Cryptocurrencies Exchange | `apiKey` | Yes | Unknown |
 | [MercadoBitcoin](https://www.mercadobitcoin.net/api-doc/) | Brazilian Cryptocurrency Information | No | Yes | Unknown |
 | [Nexchange](https://nexchange2.docs.apiary.io/) | Automated cryptocurrency exchange service | No | No | Yes |
 | [Nomics](https://nomics.com/docs/) | Historical and realtime cryptocurrency prices and market data | `apiKey` | Yes | Yes |