Add Etherescan (#2753)

README.md

@@ -214,6 +214,7 @@ API | Description | Auth | HTTPS | CORS |
 | [Chainlink](https://chain.link/developer-resources) | Build hybrid smart contracts with Chainlink | No | Yes | Unknown |
 | [Chainpoint](https://tierion.com/chainpoint/) | Chainpoint is a global network for anchoring data to the Bitcoin blockchain | No | Yes | Unknown |
 | [Covalent](https://www.covalenthq.com/docs/api/) | Multi-blockchain data aggregator platform | `apiKey` | Yes | Unknown |
+| [Etherscan](https://etherscan.io/apis) | Ethereum explorer API | `apiKey` | Yes | Yes |
 | [Nownodes](https://nownodes.io/) | Blockchain-as-a-service solution that provides high-quality connection via API | `apiKey` | Yes | Unknown |
 | [Steem](https://developers.steem.io/) | Blockchain-based blogging and social media website | No | No | No |
 | [The Graph](https://thegraph.com) | Indexing protocol for querying networks like Ethereum with GraphQL | No | Yes | Unknown |