Update README.md

Adds link to VALR's (Cryptocurrency Exchange in South Africa) API documentation

README.md

@@ -206,6 +206,7 @@ API | Description | Auth | HTTPS | CORS |
 | [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 |
 | [Poloniex](https://poloniex.com/support/api/) | US based digital asset exchange | `apiKey` | Yes | Unknown |
+| [VALR](https://docs.valr.com/) | Cryptocurrency Exchange based in South Africa | `apiKey` | Yes | Unknown |
 | [WorldCoinIndex](https://www.worldcoinindex.com/apiservice) | Cryptocurrencies Prices | `apiKey` | Yes | Unknown |
 
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