Add Watchdata to Blockchain (#3030)

README.md

@@ -233,6 +233,7 @@ API | Description | Auth | HTTPS | CORS |
 | [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 | `apiKey` | Yes | Unknown |
 | [Walltime](https://walltime.info/api.html) | To retrieve Walltime's market info | No | Yes | Unknown |
+| [Watchdata](https://docs.watchdata.io) | Provide simple and reliable API access to Ethereum blockchain | `apiKey` | Yes | Unknown |
 
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