Add CoinDesk (#2651)

README.md

@@ -344,6 +344,7 @@ API | Description | Auth | HTTPS | CORS |
 | [Coinbase Pro](https://docs.pro.coinbase.com/#api) | Cryptocurrency Trading Platform | `apiKey` | Yes | Unknown |
 | [CoinCap](https://docs.coincap.io/) | Real time Cryptocurrency prices through a RESTful API | No | Yes | Unknown |
 | [CoinDCX](https://docs.coindcx.com/) | Cryptocurrency Trading Platform | `apiKey` | Yes | Unknown |
+| [CoinDesk](https://old.coindesk.com/coindesk-api/) | CoinDesk's Bitcoin Price Index (BPI) in multiple currencies | No | Yes | 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 |
 | [Coinlib](https://coinlib.io/apidocs) | Crypto Currency Prices | `apiKey` | Yes | Unknown |