Add Helium (#2765)

README.md

@@ -215,6 +215,7 @@ API | Description | Auth | HTTPS | CORS |
 | [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 |
+| [Helium](https://docs.helium.com/api/blockchain/introduction/) | Helium is a global, distributed network of Hotspots that create public, long-range wireless coverage | No | Yes | Unknown |
 | [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 |