Add OKEx (#2842)

README.md

@@ -391,6 +391,7 @@ API | Description | Auth | HTTPS | CORS |
 | [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 |
 | [NovaDax](https://doc.novadax.com/en-US/#introduction) | NovaDAX API to access all market data, trading management endpoints | `apiKey` | Yes | Unknown |
+| [OKEx](https://www.okex.com/docs/) | Cryptocurrency exchange based in Seychelles | `apiKey` | Yes | Unknown |
 | [Poloniex](https://poloniex.com/support/api/) | US based digital asset exchange | `apiKey` | Yes | Unknown |
 | [Solana JSON RPC](https://docs.solana.com/developing/clients/jsonrpc-api) | Provides various endpoints to interact with the Solana Blockchain | No | Yes | Unknown |
 | [Technical Analysis](https://technical-analysis-api.com) | Cryptocurrency prices and technical analysis | `apiKey` | Yes | No |